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Deepest left leaf node in a binary tree | iterative approach

Given a Binary Tree, find the deepest leaf node that is left child of its parent. For example, consider the following tree. The deepest left leaf node is the node with value 9.

Examples:

```Input :
1
/   \
2     3
/      /  \
4      5    6
\     \
7     8
/       \
9         10

Output : 9```

Recursive approach to this problem is discussed here
For iterative approach, idea is similar to Method 2 of level order traversal
The idea is to traverse the tree iteratively and whenever a left tree node is pushed to queue, check if it is leaf node, if it’s leaf node, then update the result. Since we go level by level, the last stored leaf node is deepest one,

Algorithm:

• Define a Node structure that has data, left, and right pointers.
• Create a function newNode that takes data as an argument and returns a new node with data set to data, and left and right pointers set to NULL.
• Create a function getDeepestLeftLeafNode that takes the root of a binary tree as an argument and returns the deepest left leaf node of the tree.
• Initialize a queue q and add the root node of the binary tree to the queue.
• Initialize a pointer result to NULL.
• Use a while loop to traverse the binary tree level by level until the queue becomes empty.
• Within the while loop, pop the front element of the queue and store it in a temporary pointer temp.
• If temp has a left child, add it to the queue, and check if it is a leaf node (i.e., it does not have left or right child).
• If the left child of temp is a leaf node, set result to temp->left.
• If temp has a right child, add it to the queue.
• Return result which will contain the deepest left leaf node of the binary tree.
• In the main function, construct a binary tree and call getDeepestLeftLeafNode to find the deepest left leaf node of the tree.
• If result is not NULL, print the data of the deepest left leaf node, otherwise print “No result, left leaf not found”.

Implementation:

C++

 `// CPP program to find deepest left leaf``// node of binary tree``#include ``using` `namespace` `std;` `// tree node``struct` `Node {``    ``int` `data;``    ``Node *left, *right;``};` `// returns a new tree Node``Node* newNode(``int` `data)``{``    ``Node* temp = ``new` `Node();``    ``temp->data = data;``    ``temp->left = temp->right = NULL;``    ``return` `temp;``}` `// return the deepest left leaf node``// of binary tree``Node* getDeepestLeftLeafNode(Node* root)``{``    ``if` `(!root)``        ``return` `NULL;` `    ``// create a queue for level order traversal``    ``queue q;``    ``q.push(root);` `    ``Node* result = NULL;` `    ``// traverse until the queue is empty``    ``while` `(!q.empty()) {``        ``Node* temp = q.front();``        ``q.pop();` `         ` `        ``// Since we go level by level, the last``        ``// stored left leaf node is deepest one,``        ``if` `(temp->left) {``            ``q.push(temp->left);``            ``if` `(!temp->left->left && !temp->left->right)``                ``result = temp->left;``        ``}``        ` `        ``if` `(temp->right)``            ``q.push(temp->right);``    ``}``    ``return` `result;``}` `// driver program``int` `main()``{``    ``// construct a tree``    ``Node* root = newNode(1);``    ``root->left = newNode(2);``    ``root->right = newNode(3);``    ``root->left->left = newNode(4);``    ``root->right->left = newNode(5);``    ``root->right->right = newNode(6);``    ``root->right->left->right = newNode(7);``    ``root->right->right->right = newNode(8);``    ``root->right->left->right->left = newNode(9);``    ``root->right->right->right->right = newNode(10);` `    ``Node* result = getDeepestLeftLeafNode(root);``    ``if` `(result)``        ``cout << ``"Deepest Left Leaf Node :: "``             ``<< result->data << endl;``    ``else``        ``cout << ``"No result, left leaf not found\n"``;``    ``return` `0;``}`

Java

 `// Java program to find deepest left leaf``// node of binary tree``import` `java.util.*;` `public` `class` `GFG``{` `// tree node``static` `class` `Node``{``    ``int` `data;``    ``Node left, right;``};` `// returns a new tree Node``static` `Node newNode(``int` `data)``{``    ``Node temp = ``new` `Node();``    ``temp.data = data;``    ``temp.left = temp.right = ``null``;``    ``return` `temp;``}` `// return the deepest left leaf node``// of binary tree``static` `Node getDeepestLeftLeafNode(Node root)``{``    ``if` `(root == ``null``)``        ``return` `null``;` `    ``// create a queue for level order traversal``    ``Queue q = ``new` `LinkedList<>();``    ``q.add(root);` `    ``Node result = ``null``;` `    ``// traverse until the queue is empty``    ``while` `(!q.isEmpty())``    ``{``        ``Node temp = q.peek();``        ``q.remove();` `        ``// Since we go level by level, the last``        ``// stored left leaf node is deepest one,``        ``if` `(temp.left != ``null``)``        ``{``            ``q.add(temp.left);``            ``if` `(temp.left.left == ``null` `&&``                ``temp.left.right == ``null``)``                ``result = temp.left;``        ``}``        ` `        ``if` `(temp.right != ``null``)``            ``q.add(temp.right);``    ``}``    ``return` `result;``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ` `    ``// construct a tree``    ``Node root = newNode(``1``);``    ``root.left = newNode(``2``);``    ``root.right = newNode(``3``);``    ``root.left.left = newNode(``4``);``    ``root.right.left = newNode(``5``);``    ``root.right.right = newNode(``6``);``    ``root.right.left.right = newNode(``7``);``    ``root.right.right.right = newNode(``8``);``    ``root.right.left.right.left = newNode(``9``);``    ``root.right.right.right.right = newNode(``10``);` `    ``Node result = getDeepestLeftLeafNode(root);``    ``if` `(result != ``null``)``        ``System.out.println(``"Deepest Left Leaf Node :: "` `+``                                            ``result.data);``    ``else``        ``System.out.println(``"No result, "` `+``                   ``"left leaf not found"``);``    ``}``}` `// This code is contributed by Rajput-Ji`

Python3

 `# Python3 program to find deepest``# left leaf Binary search Tree` `_MIN ``=` `-``2147483648``_MAX ``=` `2147483648` `# Helper function that allocates a new``# node with the given data and None``# left and right pointers.                                    ``class` `newnode:` `    ``# Constructor to create a new node``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data``        ``self``.left ``=` `None``        ``self``.right ``=` `None` `# utility function to return deepest``# left leaf node``def` `getDeepestLeftLeafNode(root) :` `    ``if` `(``not` `root):``        ``return` `None` `    ``# create a queue for level``    ``# order traversal``    ``q ``=` `[]``    ``q.append(root)` `    ``result ``=` `None` `    ``# traverse until the queue is empty``    ``while` `(``len``(q)):``        ``temp ``=` `q[``0``]``        ``q.pop(``0``)` `        ``if` `(temp.left):``            ``q.append(temp.left)``            ``if` `(``not` `temp.left.left ``and``                ``not` `temp.left.right):``                ``result ``=` `temp.left``        ` `        ``# Since we go level by level,``        ``# the last stored right leaf``        ``# node is deepest one``        ``if` `(temp.right):``            ``q.append(temp.right)        ``    ` `    ``return` `result` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``# create a binary tree``    ``root ``=` `newnode(``1``)``    ``root.left ``=` `newnode(``2``)``    ``root.right ``=` `newnode(``3``)``    ``root.left.Left ``=` `newnode(``4``)``    ``root.right.left ``=` `newnode(``5``)``    ``root.right.right ``=` `newnode(``6``)``    ``root.right.left.right ``=` `newnode(``7``)``    ``root.right.right.right ``=` `newnode(``8``)``    ``root.right.left.right.left ``=` `newnode(``9``)``    ``root.right.right.right.right ``=` `newnode(``10``)` `    ``result ``=` `getDeepestLeftLeafNode(root)``    ``if` `result:``        ``print``(``"Deepest Left Leaf Node ::"``,``                              ``result.data)``    ``else``:``        ``print``(``"No result, Left leaf not found"``)``        ` `# This code is contributed by``# Shubham Singh(SHUBHAMSINGH10)`

C#

 `// C# program to find deepest left leaf``// node of binary tree``using` `System;``using` `System.Collections.Generic;``    ` `class` `GFG``{` `// tree node``class` `Node``{``    ``public` `int` `data;``    ``public` `Node left, right;``};` `// returns a new tree Node``static` `Node newNode(``int` `data)``{``    ``Node temp = ``new` `Node();``    ``temp.data = data;``    ``temp.left = temp.right = ``null``;``    ``return` `temp;``}` `// return the deepest left leaf node``// of binary tree``static` `Node getDeepestLeftLeafNode(Node root)``{``    ``if` `(root == ``null``)``        ``return` `null``;` `    ``// create a queue for level order traversal``    ``Queue q = ``new` `Queue();``    ``q.Enqueue(root);` `    ``Node result = ``null``;` `    ``// traverse until the queue is empty``    ``while` `(q.Count != 0)``    ``{``        ``Node temp = q.Peek();``        ``q.Dequeue();` `        ``// Since we go level by level, the last``        ``// stored left leaf node is deepest one,``        ``if` `(temp.left != ``null``)``        ``{``            ``q.Enqueue(temp.left);``            ``if` `(temp.left.left == ``null` `&&``                ``temp.left.right == ``null``)``                ``result = temp.left;``        ``}``        ``if` `(temp.right != ``null``)``            ``q.Enqueue(temp.right);``    ``}``    ``return` `result;``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ` `    ``// construct a tree``    ``Node root = newNode(1);``    ``root.left = newNode(2);``    ``root.right = newNode(3);``    ``root.left.left = newNode(4);``    ``root.right.left = newNode(5);``    ``root.right.right = newNode(6);``    ``root.right.left.right = newNode(7);``    ``root.right.right.right = newNode(8);``    ``root.right.left.right.left = newNode(9);``    ``root.right.right.right.right = newNode(10);` `    ``Node result = getDeepestLeftLeafNode(root);``    ``if` `(result != ``null``)``        ``Console.WriteLine(``"Deepest Left Leaf Node :: "` `+``                                           ``result.data);``    ``else``        ``Console.WriteLine(``"No result, "` `+``                  ``"left leaf not found"``);``    ``}``}` `// This code is contributed by Rajput-Ji`

Javascript

 ``

Output

`Deepest Left Leaf Node :: 9`

Time complexity: O(n) where n is no of nodes in a given binary tree
Auxiliary space: O(n)

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