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DFS traversal of a tree using recursion
• Difficulty Level : Easy
• Last Updated : 04 Apr, 2019

Given a Binary tree, Traverse it using DFS using recursion.

Unlike linear data structures (Array, Linked List, Queues, Stacks, etc) which have only one logical way to traverse them, trees can be traversed in different ways. Generally there are 2 widely used ways for traversing trees:

• DFS or Depth First Search
• BFS or Breadth First Search

In this article, traversal using DFS has been discussed. Please see this post for Breadth First Traversal.

### Depth-first search

DFS (Depth-first search) is technique used for traversing tree or graph. Here backtracking is used for traversal. In this traversal first the deepest node is visited and then backtracks to it’s parent node if no sibling of that node exist.

### DFS Traversal of a Graph vs Tree

In graph, there might be cycles and dis-connectivity. Unlike graph, tree does not contain cycle and always connected. So DFS of a tree is relatively easier. We can simply begin from a node, then traverse its adjacent (or children) without caring about cycles. And if we begin from a single node (root), and traverse this way, it is guaranteed that we traverse the whole tree as there is no dis-connectivity,

Examples:

```Tree: Example Tree

Therefore, the Depth First Traversals of this Tree will be:
(a) Inorder   (Left, Root, Right) : 4 2 5 1 3
(b) Preorder  (Root, Left, Right) : 1 2 4 5 3
(c) Postorder (Left, Right, Root) : 4 5 2 3 1

```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Below are the Tree traversals through DFS using recursion:

1. ## Inorder Traversal (Practice):

Example: Inorder traversal for the above-given figure is 4 2 5 1 3.

```Algorithm Inorder(tree)
1. Traverse the left subtree, i.e., call Inorder(left-subtree)
2. Visit the root.
3. Traverse the right subtree, i.e., call Inorder(right-subtree)
```

Implementation:

## C++

 `// C program for different tree traversals``#include ``using` `namespace` `std;`` ` `/* A binary tree node has data, pointer to left child``and a pointer to right child */``struct` `Node {``    ``int` `data;``    ``struct` `Node *left, *right;``    ``Node(``int` `data)``    ``{``        ``this``->data = data;``        ``left = right = NULL;``    ``}``};`` ` `/* Given a binary tree, print its nodes in inorder*/``void` `printInorder(``struct` `Node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``/* first recur on left child */``    ``printInorder(node->left);`` ` `    ``/* then print the data of node */``    ``cout << node->data << ``" "``;`` ` `    ``/* now recur on right child */``    ``printInorder(node->right);``}`` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `Node* root = ``new` `Node(1);``    ``root->left = ``new` `Node(2);``    ``root->right = ``new` `Node(3);``    ``root->left->left = ``new` `Node(4);``    ``root->left->right = ``new` `Node(5);`` ` `    ``cout << ``"\nInorder traversal of binary tree is \n"``;``    ``printInorder(root);`` ` `    ``return` `0;``}`

## C

 `// C program for different tree traversals``#include ``#include `` ` `/* A binary tree node has data, pointer to left child``   ``and a pointer to right child */``struct` `node {``    ``int` `data;``    ``struct` `node* left;``    ``struct` `node* right;``};`` ` `/* Helper function that allocates a new node with the``   ``given data and NULL left and right pointers. */``struct` `node* newNode(``int` `data)``{``    ``struct` `node* node = (``struct` `node*)``        ``malloc``(``sizeof``(``struct` `node));``    ``node->data = data;``    ``node->left = NULL;``    ``node->right = NULL;`` ` `    ``return` `(node);``}`` ` `/* Given a binary tree, print its nodes in inorder*/``void` `printInorder(``struct` `node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``/* first recur on left child */``    ``printInorder(node->left);`` ` `    ``/* then print the data of node */``    ``printf``(``"%d "``, node->data);`` ` `    ``/* now recur on right child */``    ``printInorder(node->right);``}`` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(4);``    ``root->left->right = newNode(5);`` ` `    ``printf``(``"\nInorder traversal of binary tree is \n"``);``    ``printInorder(root);`` ` `    ``getchar``();``    ``return` `0;``}`

## Java

 `// Java program for different tree traversals`` ` `/* Class containing left and right child of current``   ``node and key value*/``class` `Node {``    ``int` `key;``    ``Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``key = item;``        ``left = right = ``null``;``    ``}``}`` ` `class` `BinaryTree {``    ``// Root of Binary Tree``    ``Node root;`` ` `    ``BinaryTree()``    ``{``        ``root = ``null``;``    ``}`` ` `    ``/* Given a binary tree, print its nodes in inorder*/``    ``void` `printInorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``/* first recur on left child */``        ``printInorder(node.left);`` ` `        ``/* then print the data of node */``        ``System.out.print(node.key + ``" "``);`` ` `        ``/* now recur on right child */``        ``printInorder(node.right);``    ``}`` ` `    ``// Wrappers over above recursive functions``    ``void` `printInorder() { printInorder(root); }`` ` `    ``// Driver method``    ``public` `static` `void` `main(String[] args)``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``tree.root = ``new` `Node(``1``);``        ``tree.root.left = ``new` `Node(``2``);``        ``tree.root.right = ``new` `Node(``3``);``        ``tree.root.left.left = ``new` `Node(``4``);``        ``tree.root.left.right = ``new` `Node(``5``);`` ` `        ``System.out.println(``"\nInorder traversal of binary tree is "``);``        ``tree.printInorder();``    ``}``}`

## Python

 `# Python program to for tree traversals`` ` `# A class that represents an individual node in a``# Binary Tree``class` `Node:``    ``def` `__init__(``self``, key):``        ``self``.left ``=` `None``        ``self``.right ``=` `None``        ``self``.val ``=` `key`` ` ` ` `# A function to do inorder tree traversal``def` `printInorder(root):`` ` `    ``if` `root:`` ` `        ``# First recur on left child``        ``printInorder(root.left)`` ` `        ``# then print the data of node``        ``print``(root.val),`` ` `        ``# now recur on right child``        ``printInorder(root.right)``         ` ` ` `# Driver code``root ``=` `Node(``1``)``root.left ``=` `Node(``2``)``root.right ``=` `Node(``3``)``root.left.left ``=` `Node(``4``)``root.left.right ``=` `Node(``5``)`` ` `print` `"\nInorder traversal of binary tree is"``printInorder(root)`

## C#

 `// C# program for different tree traversals``using` `System;``     ` `/* Class containing left and right child of current``node and key value*/``class` `Node ``{``    ``public` `int` `key;``    ``public` `Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``key = item;``        ``left = right = ``null``;``    ``}``}`` ` `public` `class` `BinaryTree ``{``    ``// Root of Binary Tree``    ``Node root;`` ` `    ``BinaryTree()``    ``{``        ``root = ``null``;``    ``}`` ` `    ``/* Given a binary tree, print its nodes in inorder*/``    ``void` `printInorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``/* first recur on left child */``        ``printInorder(node.left);`` ` `        ``/* then print the data of node */``        ``Console.Write(node.key + ``" "``);`` ` `        ``/* now recur on right child */``        ``printInorder(node.right);``    ``}`` ` `    ``// Wrappers over above recursive functions``    ``void` `printInorder() ``    ``{ ``        ``printInorder(root); ``    ``}`` ` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``tree.root = ``new` `Node(1);``        ``tree.root.left = ``new` `Node(2);``        ``tree.root.right = ``new` `Node(3);``        ``tree.root.left.left = ``new` `Node(4);``        ``tree.root.left.right = ``new` `Node(5);`` ` `        ``Console.WriteLine(``"\nInorder traversal of binary tree is "``);``        ``tree.printInorder();``    ``}``}`` ` `// This code is contributed by PrinciRaj1992`
Output:
```Inorder traversal of binary tree is
4 2 5 1 3
```

Uses of Inorder:
In case of binary search trees (BST), Inorder traversal gives nodes in non-decreasing order. To get nodes of BST in non-increasing order, a variation of Inorder traversal where Inorder traversal s reversed can be used.

2. ## Preorder Traversal (Practice):

Example: Preorder traversal for the above given figure is 1 2 4 5 3.

```Algorithm Preorder(tree)
1. Visit the root.
2. Traverse the left subtree, i.e., call Preorder(left-subtree)
3. Traverse the right subtree, i.e., call Preorder(right-subtree)
```

Implementation:

## C++

 `// C program for different tree traversals``#include ``using` `namespace` `std;`` ` `/* A binary tree node has data, pointer to left child``and a pointer to right child */``struct` `Node {``    ``int` `data;``    ``struct` `Node *left, *right;``    ``Node(``int` `data)``    ``{``        ``this``->data = data;``        ``left = right = NULL;``    ``}``};`` ` `/* Given a binary tree, print its nodes in preorder*/``void` `printPreorder(``struct` `Node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``/* first print data of node */``    ``cout << node->data << ``" "``;`` ` `    ``/* then recur on left sutree */``    ``printPreorder(node->left);`` ` `    ``/* now recur on right subtree */``    ``printPreorder(node->right);``}`` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `Node* root = ``new` `Node(1);``    ``root->left = ``new` `Node(2);``    ``root->right = ``new` `Node(3);``    ``root->left->left = ``new` `Node(4);``    ``root->left->right = ``new` `Node(5);`` ` `    ``cout << ``"\nPreorder traversal of binary tree is \n"``;``    ``printPreorder(root);`` ` `    ``return` `0;``}`

## C

 `// C program for different tree traversals``#include ``#include `` ` `/* A binary tree node has data, pointer to left child``   ``and a pointer to right child */``struct` `node {``    ``int` `data;``    ``struct` `node* left;``    ``struct` `node* right;``};`` ` `/* Helper function that allocates a new node with the``   ``given data and NULL left and right pointers. */``struct` `node* newNode(``int` `data)``{``    ``struct` `node* node = (``struct` `node*)``        ``malloc``(``sizeof``(``struct` `node));``    ``node->data = data;``    ``node->left = NULL;``    ``node->right = NULL;`` ` `    ``return` `(node);``}`` ` `/* Given a binary tree, print its nodes in preorder*/``void` `printPreorder(``struct` `node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``/* first print data of node */``    ``printf``(``"%d "``, node->data);`` ` `    ``/* then recur on left sutree */``    ``printPreorder(node->left);`` ` `    ``/* now recur on right subtree */``    ``printPreorder(node->right);``}`` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(4);``    ``root->left->right = newNode(5);`` ` `    ``printf``(``"\nPreorder traversal of binary tree is \n"``);``    ``printPreorder(root);`` ` `    ``getchar``();``    ``return` `0;``}`

## Java

 `// Java program for different tree traversals`` ` `/* Class containing left and right child of current``   ``node and key value*/``class` `Node {``    ``int` `key;``    ``Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``key = item;``        ``left = right = ``null``;``    ``}``}`` ` `class` `BinaryTree {``    ``// Root of Binary Tree``    ``Node root;`` ` `    ``BinaryTree()``    ``{``        ``root = ``null``;``    ``}`` ` `    ``/* Given a binary tree, print its nodes in preorder*/``    ``void` `printPreorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``/* first print data of node */``        ``System.out.print(node.key + ``" "``);`` ` `        ``/* then recur on left sutree */``        ``printPreorder(node.left);`` ` `        ``/* now recur on right subtree */``        ``printPreorder(node.right);``    ``}`` ` `    ``// Wrappers over above recursive functions``    ``void` `printPreorder() { printPreorder(root); }`` ` `    ``// Driver method``    ``public` `static` `void` `main(String[] args)``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``tree.root = ``new` `Node(``1``);``        ``tree.root.left = ``new` `Node(``2``);``        ``tree.root.right = ``new` `Node(``3``);``        ``tree.root.left.left = ``new` `Node(``4``);``        ``tree.root.left.right = ``new` `Node(``5``);`` ` `        ``System.out.println(``"Preorder traversal of binary tree is "``);``        ``tree.printPreorder();``    ``}``}`

## Python

 `# Python program to for tree traversals`` ` `# A class that represents an individual node in a``# Binary Tree``class` `Node:``    ``def` `__init__(``self``, key):``        ``self``.left ``=` `None``        ``self``.right ``=` `None``        ``self``.val ``=` `key`` ` `# A function to do preorder tree traversal``def` `printPreorder(root):`` ` `    ``if` `root:`` ` `        ``# First print the data of node``        ``print``(root.val),`` ` `        ``# Then recur on left child``        ``printPreorder(root.left)`` ` `        ``# Finally recur on right child``        ``printPreorder(root.right)`` ` ` ` `# Driver code``root ``=` `Node(``1``)``root.left ``=` `Node(``2``)``root.right ``=` `Node(``3``)``root.left.left ``=` `Node(``4``)``root.left.right ``=` `Node(``5``)``print` `"Preorder traversal of binary tree is"``printPreorder(root)`

## C#

 `// C# program for different tree traversals``using` `System;`` ` `/* Class containing left and right child of current``node and key value*/``public` `class` `Node ``{``    ``public` `int` `key;``    ``public` `Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``key = item;``        ``left = right = ``null``;``    ``}``}`` ` `public` `class` `BinaryTree ``{``    ``// Root of Binary Tree``    ``Node root;`` ` `    ``BinaryTree()``    ``{``        ``root = ``null``;``    ``}`` ` `    ``/* Given a binary tree, print its nodes in preorder*/``    ``void` `printPreorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``/* first print data of node */``        ``Console.Write(node.key + ``" "``);`` ` `        ``/* then recur on left sutree */``        ``printPreorder(node.left);`` ` `        ``/* now recur on right subtree */``        ``printPreorder(node.right);``    ``}`` ` `    ``// Wrappers over above recursive functions``    ``void` `printPreorder() { printPreorder(root); }`` ` `    ``// Driver method``    ``public` `static` `void` `Main()``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``tree.root = ``new` `Node(1);``        ``tree.root.left = ``new` `Node(2);``        ``tree.root.right = ``new` `Node(3);``        ``tree.root.left.left = ``new` `Node(4);``        ``tree.root.left.right = ``new` `Node(5);`` ` `        ``Console.WriteLine(``"Preorder traversal of binary tree is "``);``        ``tree.printPreorder();``    ``}``}`` ` `/* This code contributed by PrinciRaj1992 */`
Output:
```Preorder traversal of binary tree is
1 2 4 5 3
```

Uses of Preorder:
Preorder traversal is used to create a copy of the tree. Preorder traversal is also used to get prefix expression on of an expression tree. Please see http://en.wikipedia.org/wiki/Polish_notation to know why prefix expressions are useful.

3. ## Postorder Traversal (Practice):

Example: Postorder traversal for the above given Tree is 4 5 2 3 1.

```Algorithm Postorder(tree)
1. Traverse the left subtree, i.e., call Postorder(left-subtree)
2. Traverse the right subtree, i.e., call Postorder(right-subtree)
3. Visit the root.
```

Implementation:

## C++

 `// C program for different tree traversals``#include ``using` `namespace` `std;`` ` `/* A binary tree node has data, pointer to left child``and a pointer to right child */``struct` `Node {``    ``int` `data;``    ``struct` `Node *left, *right;``    ``Node(``int` `data)``    ``{``        ``this``->data = data;``        ``left = right = NULL;``    ``}``};`` ` `/* Given a binary tree, print its nodes according to the``"bottom-up" postorder traversal. */``void` `printPostorder(``struct` `Node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``// first recur on left subtree``    ``printPostorder(node->left);`` ` `    ``// then recur on right subtree``    ``printPostorder(node->right);`` ` `    ``// now deal with the node``    ``cout << node->data << ``" "``;``}`` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `Node* root = ``new` `Node(1);``    ``root->left = ``new` `Node(2);``    ``root->right = ``new` `Node(3);``    ``root->left->left = ``new` `Node(4);``    ``root->left->right = ``new` `Node(5);`` ` `    ``cout << ``"\nPostorder traversal of binary tree is \n"``;``    ``printPostorder(root);`` ` `    ``return` `0;``}`

## C

 `// C program for different tree traversals``#include ``#include `` ` `/* A binary tree node has data, pointer to left child``   ``and a pointer to right child */``struct` `node {``    ``int` `data;``    ``struct` `node* left;``    ``struct` `node* right;``};`` ` `/* Helper function that allocates a new node with the``   ``given data and NULL left and right pointers. */``struct` `node* newNode(``int` `data)``{``    ``struct` `node* node = (``struct` `node*)``        ``malloc``(``sizeof``(``struct` `node));``    ``node->data = data;``    ``node->left = NULL;``    ``node->right = NULL;`` ` `    ``return` `(node);``}`` ` `/* Given a binary tree, print its nodes according to the``  ``"bottom-up" postorder traversal. */``void` `printPostorder(``struct` `node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``// first recur on left subtree``    ``printPostorder(node->left);`` ` `    ``// then recur on right subtree``    ``printPostorder(node->right);`` ` `    ``// now deal with the node``    ``printf``(``"%d "``, node->data);``}`` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(4);``    ``root->left->right = newNode(5);`` ` `    ``printf``(``"\nPostorder traversal of binary tree is \n"``);``    ``printPostorder(root);`` ` `    ``getchar``();``    ``return` `0;``}`

## Java

 `// Java program for different tree traversals`` ` `/* Class containing left and right child of current``   ``node and key value*/``class` `Node {``    ``int` `key;``    ``Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``key = item;``        ``left = right = ``null``;``    ``}``}`` ` `class` `BinaryTree {``    ``// Root of Binary Tree``    ``Node root;`` ` `    ``BinaryTree()``    ``{``        ``root = ``null``;``    ``}`` ` `    ``/* Given a binary tree, print its nodes according to the``      ``"bottom-up" postorder traversal. */``    ``void` `printPostorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``// first recur on left subtree``        ``printPostorder(node.left);`` ` `        ``// then recur on right subtree``        ``printPostorder(node.right);`` ` `        ``// now deal with the node``        ``System.out.print(node.key + ``" "``);``    ``}`` ` `    ``// Wrappers over above recursive functions``    ``void` `printPostorder() { printPostorder(root); }`` ` `    ``// Driver method``    ``public` `static` `void` `main(String[] args)``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``tree.root = ``new` `Node(``1``);``        ``tree.root.left = ``new` `Node(``2``);``        ``tree.root.right = ``new` `Node(``3``);``        ``tree.root.left.left = ``new` `Node(``4``);``        ``tree.root.left.right = ``new` `Node(``5``);`` ` `        ``System.out.println(``"\nPostorder traversal of binary tree is "``);``        ``tree.printPostorder();``    ``}``}`

## Python

 `# Python program to for tree traversals`` ` `# A class that represents an individual node in a``# Binary Tree``class` `Node:``    ``def` `__init__(``self``, key):``        ``self``.left ``=` `None``        ``self``.right ``=` `None``        ``self``.val ``=` `key`` ` `         ` `# A function to do postorder tree traversal``def` `printPostorder(root):`` ` `    ``if` `root:`` ` `        ``# First recur on left child``        ``printPostorder(root.left)`` ` `        ``# the recur on right child``        ``printPostorder(root.right)`` ` `        ``# now print the data of node``        ``print``(root.val),`` ` ` ` `# Driver code``root ``=` `Node(``1``)``root.left ``=` `Node(``2``)``root.right ``=` `Node(``3``)``root.left.left ``=` `Node(``4``)``root.left.right ``=` `Node(``5``)`` ` `print` `"\nPostorder traversal of binary tree is"``printPostorder(root)`

## C#

 `// C# program for different tree traversals``using` `System;`` ` `/* Class containing left and right child of current``node and key value*/``public` `class` `Node ``{``    ``public` `int` `key;``    ``public` `Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``key = item;``        ``left = right = ``null``;``    ``}``}`` ` `public` `class` `BinaryTree ``{``    ``// Root of Binary Tree``    ``Node root;`` ` `    ``BinaryTree()``    ``{``        ``root = ``null``;``    ``}`` ` `    ``/* Given a binary tree, print its nodes according to the``    ``"bottom-up" postorder traversal. */``    ``void` `printPostorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``// first recur on left subtree``        ``printPostorder(node.left);`` ` `        ``// then recur on right subtree``        ``printPostorder(node.right);`` ` `        ``// now deal with the node``        ``Console.Write(node.key + ``" "``);``    ``}`` ` `    ``// Wrappers over above recursive functions``    ``void` `printPostorder() { printPostorder(root); }`` ` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``tree.root = ``new` `Node(1);``        ``tree.root.left = ``new` `Node(2);``        ``tree.root.right = ``new` `Node(3);``        ``tree.root.left.left = ``new` `Node(4);``        ``tree.root.left.right = ``new` `Node(5);`` ` `        ``Console.WriteLine(``"\nPostorder traversal of binary tree is "``);``        ``tree.printPostorder();``    ``}``}`` ` `// This code contributed by Rajput-Ji`
Output:
```Postorder traversal of binary tree is
4 5 2 3 1
```

Uses of Postorder:
Postorder traversal is used to delete the tree. Please see the question for deletion of tree for details. Postorder traversal is also useful to get the postfix expression of an expression tree. Please see http://en.wikipedia.org/wiki/Reverse_Polish_notation to for the usage of postfix expression.

## C++

 `// C program for different tree traversals``#include ``using` `namespace` `std;`` ` `/* A binary tree node has data, pointer to left child``and a pointer to right child */``struct` `Node``{``    ``int` `data;``    ``struct` `Node* left, *right;``    ``Node(``int` `data)``    ``{``        ``this``->data = data;``        ``left = right = NULL;``    ``}``};`` ` `/* Given a binary tree, print its nodes according to the``"bottom-up" postorder traversal. */``void` `printPostorder(``struct` `Node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``// first recur on left subtree``    ``printPostorder(node->left);`` ` `    ``// then recur on right subtree``    ``printPostorder(node->right);`` ` `    ``// now deal with the node``    ``cout << node->data << ``" "``;``}`` ` `/* Given a binary tree, print its nodes in inorder*/``void` `printInorder(``struct` `Node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``/* first recur on left child */``    ``printInorder(node->left);`` ` `    ``/* then print the data of node */``    ``cout << node->data << ``" "``;`` ` `    ``/* now recur on right child */``    ``printInorder(node->right);``}`` ` `/* Given a binary tree, print its nodes in preorder*/``void` `printPreorder(``struct` `Node* node)``{``    ``if` `(node == NULL)``        ``return``;`` ` `    ``/* first print data of node */``    ``cout << node->data << ``" "``;`` ` `    ``/* then recur on left sutree */``    ``printPreorder(node->left); `` ` `    ``/* now recur on right subtree */``    ``printPreorder(node->right);``} `` ` `/* Driver program to test above functions*/``int` `main()``{``    ``struct` `Node *root = ``new` `Node(1);``    ``root->left             = ``new` `Node(2);``    ``root->right         = ``new` `Node(3);``    ``root->left->left     = ``new` `Node(4);``    ``root->left->right = ``new` `Node(5); `` ` `    ``cout << ``"\nPreorder traversal of binary tree is \n"``;``    ``printPreorder(root);`` ` `    ``cout << ``"\nInorder traversal of binary tree is \n"``;``    ``printInorder(root); `` ` `    ``cout << ``"\nPostorder traversal of binary tree is \n"``;``    ``printPostorder(root);`` ` `    ``return` `0;``}`

## C

 `// C program for different tree traversals``#include ``#include `` ` `/* A binary tree node has data, pointer to left child``   ``and a pointer to right child */``struct` `node``{``     ``int` `data;``     ``struct` `node* left;``     ``struct` `node* right;``};`` ` `/* Helper function that allocates a new node with the``   ``given data and NULL left and right pointers. */``struct` `node* newNode(``int` `data)``{``     ``struct` `node* node = (``struct` `node*)``                                  ``malloc``(``sizeof``(``struct` `node));``     ``node->data = data;``     ``node->left = NULL;``     ``node->right = NULL;`` ` `     ``return``(node);``}`` ` `/* Given a binary tree, print its nodes according to the``  ``"bottom-up" postorder traversal. */``void` `printPostorder(``struct` `node* node)``{``     ``if` `(node == NULL)``        ``return``;`` ` `     ``// first recur on left subtree``     ``printPostorder(node->left);`` ` `     ``// then recur on right subtree``     ``printPostorder(node->right);`` ` `     ``// now deal with the node``     ``printf``(``"%d "``, node->data);``}`` ` `/* Given a binary tree, print its nodes in inorder*/``void` `printInorder(``struct` `node* node)``{``     ``if` `(node == NULL)``          ``return``;`` ` `     ``/* first recur on left child */``     ``printInorder(node->left);`` ` `     ``/* then print the data of node */``     ``printf``(``"%d "``, node->data);  `` ` `     ``/* now recur on right child */``     ``printInorder(node->right);``}`` ` `/* Given a binary tree, print its nodes in preorder*/``void` `printPreorder(``struct` `node* node)``{``     ``if` `(node == NULL)``          ``return``;`` ` `     ``/* first print data of node */``     ``printf``(``"%d "``, node->data);  `` ` `     ``/* then recur on left sutree */``     ``printPreorder(node->left);  `` ` `     ``/* now recur on right subtree */``     ``printPreorder(node->right);``}    `` ` `/* Driver program to test above functions*/``int` `main()``{``     ``struct` `node *root  = newNode(1);``     ``root->left             = newNode(2);``     ``root->right           = newNode(3);``     ``root->left->left     = newNode(4);``     ``root->left->right   = newNode(5); `` ` `     ``printf``(``"\nPreorder traversal of binary tree is \n"``);``     ``printPreorder(root);`` ` `     ``printf``(``"\nInorder traversal of binary tree is \n"``);``     ``printInorder(root);  `` ` `     ``printf``(``"\nPostorder traversal of binary tree is \n"``);``     ``printPostorder(root);`` ` `     ``getchar``();``     ``return` `0;``}`

## Java

 `// Java program for different tree traversals`` ` `/* Class containing left and right child of current``   ``node and key value*/``class` `Node``{``    ``int` `key;``    ``Node left, right;`` ` `    ``public` `Node(``int` `item)``    ``{``        ``key = item;``        ``left = right = ``null``;``    ``}``}`` ` `class` `BinaryTree``{``    ``// Root of Binary Tree``    ``Node root;`` ` `    ``BinaryTree()``    ``{``        ``root = ``null``;``    ``}`` ` `    ``/* Given a binary tree, print its nodes according to the``      ``"bottom-up" postorder traversal. */``    ``void` `printPostorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``// first recur on left subtree``        ``printPostorder(node.left);`` ` `        ``// then recur on right subtree``        ``printPostorder(node.right);`` ` `        ``// now deal with the node``        ``System.out.print(node.key + ``" "``);``    ``}`` ` `    ``/* Given a binary tree, print its nodes in inorder*/``    ``void` `printInorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``/* first recur on left child */``        ``printInorder(node.left);`` ` `        ``/* then print the data of node */``        ``System.out.print(node.key + ``" "``);`` ` `        ``/* now recur on right child */``        ``printInorder(node.right);``    ``}`` ` `    ``/* Given a binary tree, print its nodes in preorder*/``    ``void` `printPreorder(Node node)``    ``{``        ``if` `(node == ``null``)``            ``return``;`` ` `        ``/* first print data of node */``        ``System.out.print(node.key + ``" "``);`` ` `        ``/* then recur on left sutree */``        ``printPreorder(node.left);`` ` `        ``/* now recur on right subtree */``        ``printPreorder(node.right);``    ``}`` ` `    ``// Wrappers over above recursive functions``    ``void` `printPostorder()  {     printPostorder(root);  }``    ``void` `printInorder()    {     printInorder(root);   }``    ``void` `printPreorder()   {     printPreorder(root);  }`` ` `    ``// Driver method``    ``public` `static` `void` `main(String[] args)``    ``{``        ``BinaryTree tree = ``new` `BinaryTree();``        ``tree.root = ``new` `Node(``1``);``        ``tree.root.left = ``new` `Node(``2``);``        ``tree.root.right = ``new` `Node(``3``);``        ``tree.root.left.left = ``new` `Node(``4``);``        ``tree.root.left.right = ``new` `Node(``5``);`` ` `        ``System.out.println(``"Preorder traversal of binary tree is "``);``        ``tree.printPreorder();`` ` `        ``System.out.println(``"\nInorder traversal of binary tree is "``);``        ``tree.printInorder();`` ` `        ``System.out.println(``"\nPostorder traversal of binary tree is "``);``        ``tree.printPostorder();``    ``}``}`

## Python

 `# Python program to for tree traversals`` ` `# A class that represents an individual node in a``# Binary Tree``class` `Node:``    ``def` `__init__(``self``,key):``        ``self``.left ``=` `None``        ``self``.right ``=` `None``        ``self``.val ``=` `key`` ` ` ` `# A function to do inorder tree traversal``def` `printInorder(root):`` ` `    ``if` `root:`` ` `        ``# First recur on left child``        ``printInorder(root.left)`` ` `        ``# then print the data of node``        ``print``(root.val),`` ` `        ``# now recur on right child``        ``printInorder(root.right)`` ` ` ` ` ` `# A function to do postorder tree traversal``def` `printPostorder(root):`` ` `    ``if` `root:`` ` `        ``# First recur on left child``        ``printPostorder(root.left)`` ` `        ``# the recur on right child``        ``printPostorder(root.right)`` ` `        ``# now print the data of node``        ``print``(root.val),`` ` ` ` `# A function to do preorder tree traversal``def` `printPreorder(root):`` ` `    ``if` `root:`` ` `        ``# First print the data of node``        ``print``(root.val),`` ` `        ``# Then recur on left child``        ``printPreorder(root.left)`` ` `        ``# Finally recur on right child``        ``printPreorder(root.right)`` ` ` ` `# Driver code``root ``=` `Node(``1``)``root.left      ``=` `Node(``2``)``root.right     ``=` `Node(``3``)``root.left.left  ``=` `Node(``4``)``root.left.right  ``=` `Node(``5``)``print` `"Preorder traversal of binary tree is"``printPreorder(root)`` ` `print` `"\nInorder traversal of binary tree is"``printInorder(root)`` ` `print` `"\nPostorder traversal of binary tree is"``printPostorder(root)`

## C#

 `// C# program for different Console.Writetree traversals `` ` `using` `System;`` ` `/* Class containing left and right child of current ``node and key value*/``public` `class` `Node ``{ ``    ``public` `int` `key; ``    ``public` `Node left, right; `` ` `    ``public` `Node(``int` `item) ``    ``{ ``        ``key = item; ``        ``left = right = ``null``; ``    ``} ``} `` ` `public` `class` `BinaryTree ``{ ``    ``// Root of Binary Tree ``    ``Node root; `` ` `    ``BinaryTree() ``    ``{ ``        ``root = ``null``; ``    ``} `` ` `    ``/* Given a binary tree, print ``    ``its nodes according to the ``    ``"bottom-up" postorder traversal. */``    ``void` `printPostorder(Node node) ``    ``{ ``        ``if` `(node == ``null``) ``            ``return``; `` ` `        ``// first recur on left subtree ``        ``printPostorder(node.left); `` ` `        ``// then recur on right subtree ``        ``printPostorder(node.right); `` ` `        ``// now deal with the node ``        ``Console.Write(node.key + ``" "``); ``    ``} `` ` `    ``/* Given a binary tree, print its nodes in inorder*/``    ``void` `printInorder(Node node) ``    ``{ ``        ``if` `(node == ``null``) ``            ``return``; `` ` `        ``/* first recur on left child */``        ``printInorder(node.left); `` ` `        ``/* then print the data of node */``        ``Console.Write(node.key + ``" "``); `` ` `        ``/* now recur on right child */``        ``printInorder(node.right); ``    ``} `` ` `    ``/* Given a binary tree, print its nodes in preorder*/``    ``void` `printPreorder(Node node) ``    ``{ ``        ``if` `(node == ``null``) ``            ``return``; `` ` `        ``/* first print data of node */``        ``Console.Write(node.key + ``" "``); `` ` `        ``/* then recur on left sutree */``        ``printPreorder(node.left); `` ` `        ``/* now recur on right subtree */``        ``printPreorder(node.right); ``    ``} `` ` `    ``// Wrappers over above recursive functions ``    ``void` `printPostorder() { printPostorder(root); } ``    ``void` `printInorder() { printInorder(root); } ``    ``void` `printPreorder() { printPreorder(root); } `` ` `    ``// Driver code ``    ``public` `static` `void` `Main(String[] args) ``    ``{ ``        ``BinaryTree tree = ``new` `BinaryTree(); ``        ``tree.root = ``new` `Node(1); ``        ``tree.root.left = ``new` `Node(2); ``        ``tree.root.right = ``new` `Node(3); ``        ``tree.root.left.left = ``new` `Node(4); ``        ``tree.root.left.right = ``new` `Node(5); `` ` `        ``Console.WriteLine(``"Preorder traversal of binary tree is "``); ``        ``tree.printPreorder(); `` ` `        ``Console.WriteLine(``"\nInorder traversal of binary tree is "``); ``        ``tree.printInorder(); `` ` `        ``Console.WriteLine(``"\nPostorder traversal of binary tree is "``); ``        ``tree.printPostorder(); ``    ``} ``} `` ` `// This code has been contributed by 29AjayKumar`

Output:
```Preorder traversal of binary tree is
1 2 4 5 3
Inorder traversal of binary tree is
4 2 5 1 3
Postorder traversal of binary tree is
4 5 2 3 1```

Time Complexity: O(n)
Auxiliary Space : If we don’t consider size of stack for function calls then O(1) otherwise O(n).

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