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Bottom View of a Binary Tree using Recursion
• Difficulty Level : Medium
• Last Updated : 15 Dec, 2020

Given a binary tree, the task is to find the bottom view of a binary tree using recursion.

Examples:

```Input:
1
\
2
\
4
/  \
3    5
Output: 1 3 4 5

Input:
20
/    \
8       22
/   \    /   \
5      10 21     25
/ \
9    14

Output: 5 9 21 14 25```

Approach:
We can do so by using recursion and 2 arrays each with size 2n+1(for worst case), where n = number of elements in the given tree. Here, we take a Variable x which determines its Horizontal Distance. Let x is the horizontal distance of a Node. Now, the left child will have a horizontal distance of x-1(x minus 1)and the right child will have horizontal distance x+1(x plus 1). Take another Variable ‘p’ as a priority which will decide which level this element belongs to.

```    1 (x=0, p=0)
\
2 (x=1, p=1)
\
4 (x=2, p=2)
/  \
(x=1, p=3) 3     5 (x=3, p=3)```

While Traversing the Tree In fashion Right-> Node-> Left, assign x and p to each Node and simultaneously insert the data of node in the first array if the array is empty at position (mid+x). If the array is not empty and a Node with higher Priority( p ) comes to update the array with the data of this Node as position(mid+x). The second array will be maintaining the priority( p ) of each inserted node in the first array check code for better understanding.

Below is the implementation of above approach:

## C++

 `#include ``using` `namespace` `std;` `struct` `Node {``    ``int` `data;``    ``// left and right references``    ``Node *left, *right;``    ``// Constructor of tree Node``    ``Node(``int` `key)``    ``{``        ``data = key;``        ``left = right = NULL;``    ``}``};` `int` `l = 0, r = 0;``int` `N;` `// Function to generate``// bottom view of``// binary tree``void` `Bottom(Node* root, ``int` `arr[], ``int` `arr2[], ``int` `x, ``int` `p, ``int` `mid)``{``    ``// Base case``    ``if` `(root == NULL) {``        ``return``;``    ``}` `    ``if` `(x < l) {``        ``// To store leftmost``        ``// value of x in l``        ``l = x;``    ``}` `    ``// To store rightmost``    ``// value of x in r``    ``if` `(x > r) {``        ``r = x;``    ``}` `    ``// To check if arr``    ``// is empty at mid+x``    ``if` `(arr[mid + x] == INT_MIN) {``        ``// Insert data of Node``        ``// at arr[mid+x]``        ``arr[mid + x] = root->data;``        ``// Insert priority of``        ``// that Node at arr2[mid+x]``        ``arr2[mid + x] = p;``    ``}` `    ``// If not empty and priotiy``    ``// of previously inserted``    ``// Node is less than current*/``    ``else` `if` `(arr2[mid + x] < p) {``        ``// Insert current``        ``// Node data at arr[mid+x]``        ``arr[mid + x] = root->data;` `        ``// Insert priotiy of``        ``// that Node at arr2[mid +x]``        ``arr2[mid + x] = p;``    ``}` `    ``// Go right first``    ``// then left``    ``Bottom(root->right, arr, arr2, x + 1, p + 1, mid);``    ``Bottom(root->left, arr, arr2, x - 1, p + 1, mid);``}` `// Utility function``// to generate bottom``// view of a biany tree``void` `bottomView(``struct` `Node* root)``{``    ``int` `arr[2 * N + 1];``    ``int` `arr2[2 * N + 1];` `    ``for` `(``int` `i = 0; i < 2 * N + 1; i++) {``        ``arr[i] = INT_MIN;``        ``arr2[i] = INT_MIN;``    ``}` `    ``int` `mid = N, x = 0, p = 0;` `    ``Bottom(root, arr, arr2, x, p, mid);` `    ``for` `(``int` `i = mid + l; i <= mid + r; i++) {``        ``cout << arr[i] << ``" "``;``    ``}``}` `// Driver code``int` `main()``{` `    ``N = 5;``    ``Node* root = ``new` `Node(1);``    ``root->right = ``new` `Node(2);``    ``root->right->right = ``new` `Node(4);``    ``root->right->right->left = ``new` `Node(3);``    ``root->right->right->right = ``new` `Node(5);` `    ``bottomView(root);` `    ``return` `0;``}`

## Java

 `class` `GFG{``    ` `static` `class` `Node``{``    ``int` `data;``    ` `    ``// left and right references``    ``Node left, right;``    ` `    ``// Constructor of tree Node``    ``public` `Node(``int` `key)``    ``{``        ``data = key;``        ``left = right = ``null``;``    ``}``};` `static` `int` `l = ``0``, r = ``0``, N;` `// Function to generate``// bottom view of binary tree``static` `void` `Bottom(Node root, ``int` `arr[],``                  ``int` `arr2[], ``int` `x,``                       ``int` `p, ``int` `mid)``{``    ` `    ``// Base case``    ``if` `(root == ``null``)``    ``{``        ``return``;``    ``}` `    ``if` `(x < l)``    ``{``        ` `        ``// To store leftmost``        ``// value of x in l``        ``l = x;``    ``}` `    ``// To store rightmost``    ``// value of x in r``    ``if` `(x > r)``    ``{``        ``r = x;``    ``}` `    ``// To check if arr``    ``// is empty at mid+x``    ``if` `(arr[mid + x] == Integer.MIN_VALUE)``    ``{``        ` `        ``// Insert data of Node``        ``// at arr[mid+x]``        ``arr[mid + x] = root.data;``        ` `        ``// Insert priority of``        ``// that Node at arr2[mid+x]``        ``arr2[mid + x] = p;``    ``}` `    ``// If not empty and priotiy``    ``// of previously inserted``    ``// Node is less than current*/``    ``else` `if` `(arr2[mid + x] < p)``    ``{``        ` `        ``// Insert current``        ``// Node data at arr[mid+x]``        ``arr[mid + x] = root.data;` `        ``// Insert priotiy of``        ``// that Node at arr2[mid +x]``        ``arr2[mid + x] = p;``    ``}` `    ``// Go right first``    ``// then left``    ``Bottom(root.right, arr, arr2,``           ``x + ``1``, p + ``1``, mid);``    ``Bottom(root.left, arr, arr2,``           ``x - ``1``, p + ``1``, mid);``}` `// Utility function to generate``// bottom view of a biany tree``static` `void` `bottomView(Node root)``{``    ``int``[] arr = ``new` `int``[``2` `* N + ``1``];``    ``int``[] arr2 = ``new` `int``[``2` `* N + ``1``];` `    ``for``(``int` `i = ``0``; i < ``2` `* N + ``1``; i++)``    ``{``        ``arr[i] = Integer.MIN_VALUE;``        ``arr2[i] = Integer.MIN_VALUE;``    ``}` `    ``int` `mid = N, x = ``0``, p = ``0``;` `    ``Bottom(root, arr, arr2, x, p, mid);` `    ``for``(``int` `i = mid + l; i <= mid + r; i++)``    ``{``        ``System.out.print(arr[i] + ``" "``);``    ``}``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``N = ``5``;``    ` `    ``Node root = ``new` `Node(``1``);``    ``root.right = ``new` `Node(``2``);``    ``root.right.right = ``new` `Node(``4``);``    ``root.right.right.left = ``new` `Node(``3``);``    ``root.right.right.right = ``new` `Node(``5``);` `    ``bottomView(root);``}``}` `// This code is contributed by sanjeev2552`

## Python3

 `class` `Node:``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data``        ``self``.left ``=` `None``        ``self``.right ``=` `None` `l ``=` `0``r ``=` `0``INT_MIN ``=` `-``(``2``*``*``32``)` `# Function to generate``# bottom view of``# binary tree``def` `Bottom(root, arr, arr2, x, p, mid):``    ``global` `INT_MIN, l, r``    ` `    ``# Base case``    ``if` `(root ``=``=` `None``):``        ``return``    ` `    ``if` `(x < l):``        ` `        ``# To store leftmost``        ``# value of x in l``        ``l ``=` `x``    ` `    ``# To store rightmost``    ``# value of x in r``    ``if` `(x > r):``        ``r ``=` `x``        ` `    ``# To check if arr``    ``# is empty at mid+x``    ``if` `(arr[mid ``+` `x] ``=``=` `INT_MIN):` `        ``# Insert data of Node``        ``# at arr[mid+x]``        ``arr[mid ``+` `x] ``=` `root.data` `        ``# Insert priority of``        ``# that Node at arr2[mid+x]``        ``arr2[mid ``+` `x] ``=` `p``        ` `    ``# If not empty and priotiy``    ``# of previously inserted``    ``# Node is less than current*/``    ``elif` `(arr2[mid ``+` `x] < p):` `        ``# Insert current``        ``# Node data at arr[mid+x]``        ``arr[mid ``+` `x] ``=` `root.data``        ` `        ``# Insert priotiy of``        ``# that Node at arr2[mid +x]``        ``arr2[mid ``+` `x] ``=` `p``    ` `    ``# Go right first``    ``# then left``    ``Bottom(root.right, arr, arr2, x ``+` `1``, p ``+` `1``, mid)``    ``Bottom(root.left, arr, arr2, x ``-` `1``, p ``+` `1``, mid)` `# Utility function``# to generate bottom``# view of a biany tree``def` `bottomView(root):``    ``global` `INT_MIN``    ``arr ``=` `[``0``]``*``(``2` `*` `N ``+` `1``)``    ``arr2 ``=` `[``0``]``*``(``2` `*` `N ``+` `1``)``    ` `    ``for` `i ``in` `range``(``2` `*` `N ``+` `1``):``        ``arr[i] ``=` `INT_MIN``        ``arr2[i] ``=` `INT_MIN``    ``mid ``=` `N``    ``x ``=` `0``    ``p ``=` `0``    ``Bottom(root, arr, arr2, x, p, mid)``    ` `    ``for` `i ``in` `range``(mid ``+` `l,mid ``+` `r ``+` `1``):``        ``print``(arr[i], end ``=` `" "``)``        ` `# Driver code``N ``=` `5``root ``=` `Node(``1``)``root.right ``=` `Node(``2``)``root.right.right ``=` `Node(``4``)``root.right.right.left ``=` `Node(``3``)``root.right.right.right ``=` `Node(``5``)` `bottomView(root)``    ` `# This code is contributed by SHUBHAMSINGH10`

## C#

 `using` `System;` `class` `GFG{``    ` `class` `Node{``    ` `public` `int` `data;` `// left and right references``public` `Node left, right;` `// Constructor of tree Node``public` `Node(``int` `key)``{``    ``data = key;``    ``left = right = ``null``;``}``};` `static` `int` `l = 0, r = 0, N;` `// Function to generate``// bottom view of binary tree``static` `void` `Bottom(Node root, ``int` `[]arr,``                  ``int` `[]arr2, ``int` `x,``                       ``int` `p, ``int` `mid)``{``    ` `    ``// Base case``    ``if` `(root == ``null``)``    ``{``        ``return``;``    ``}` `    ``if` `(x < l)``    ``{``        ` `        ``// To store leftmost``        ``// value of x in l``        ``l = x;``    ``}` `    ``// To store rightmost``    ``// value of x in r``    ``if` `(x > r)``    ``{``        ``r = x;``    ``}` `    ``// To check if arr``    ``// is empty at mid+x``    ``if` `(arr[mid + x] == Int32.MinValue)``    ``{``        ` `        ``// Insert data of Node``        ``// at arr[mid+x]``        ``arr[mid + x] = root.data;``        ` `        ``// Insert priority of``        ``// that Node at arr2[mid+x]``        ``arr2[mid + x] = p;``    ``}` `    ``// If not empty and priotiy``    ``// of previously inserted``    ``// Node is less than current*/``    ``else` `if` `(arr2[mid + x] < p)``    ``{``        ` `        ``// Insert current``        ``// Node data at arr[mid+x]``        ``arr[mid + x] = root.data;` `        ``// Insert priotiy of``        ``// that Node at arr2[mid +x]``        ``arr2[mid + x] = p;``    ``}` `    ``// Go right first``    ``// then left``    ``Bottom(root.right, arr, arr2,``           ``x + 1, p + 1, mid);``    ``Bottom(root.left, arr, arr2,``           ``x - 1, p + 1, mid);``}` `// Utility function to generate``// bottom view of a biany tree``static` `void` `bottomView(Node root)``{``    ``int``[] arr = ``new` `int``[2 * N + 1];``    ``int``[] arr2 = ``new` `int``[2 * N + 1];` `    ``for``(``int` `i = 0; i < 2 * N + 1; i++)``    ``{``        ``arr[i] = Int32.MinValue;``        ``arr2[i] = Int32.MinValue;``    ``}` `    ``int` `mid = N, x = 0, p = 0;` `    ``Bottom(root, arr, arr2, x, p, mid);` `    ``for``(``int` `i = mid + l; i <= mid + r; i++)``    ``{``        ``Console.Write(arr[i] + ``" "``);``    ``}``}` `// Driver code``public` `static` `void` `Main(``string``[] args)``{``    ``N = 5;``    ` `    ``Node root = ``new` `Node(1);``    ``root.right = ``new` `Node(2);``    ``root.right.right = ``new` `Node(4);``    ``root.right.right.left = ``new` `Node(3);``    ``root.right.right.right = ``new` `Node(5);` `    ``bottomView(root);``}``}` `// This code is contributed by rutvik_56`
Output:
`1 3 4 5`

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