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Largest number less than or equal to N in BST (Iterative Approach)
• Difficulty Level : Easy
• Last Updated : 04 Nov, 2020

We have a binary search tree and a number N. Our task is to find the greatest number in the binary search tree that is less than or equal to N. Print the value of the element if it exists otherwise print -1.

Examples: For the above given binary search tree-

```Input : N = 24
Output :result = 21
(searching for 24 will be like-5->12->21)

Input  : N = 4
Output : result = 3
(searching for 4 will be like-5->2->3)
```

We have discussed recursive approach in below post.
Largest number in BST which is less than or equal to N
Here an iterative approach is discussed. We try to find the predecessor of the target. Keep two pointers, one pointing to the current node and one for storing the answer. If the current node’s data > N, we move towards left. In other case, when current node’s data is less than N, the current node can be our answer (so far), and we move towards right.

## C++

 `// C++ code to find the largest value smaller``// than or equal to N``#include ``using` `namespace` `std;`` ` `struct` `Node {``    ``int` `key;``    ``Node *left, *right;``};`` ` `// To create new BST Node``Node* newNode(``int` `item)``{``    ``Node* temp = ``new` `Node;``    ``temp->key = item;``    ``temp->left = temp->right = NULL;``    ``return` `temp;``}`` ` `// To insert a new node in BST``Node* insert(Node* node, ``int` `key)``{``    ``// if tree is empty return new node``    ``if` `(node == NULL)``        ``return` `newNode(key);`` ` `    ``// if key is less then or grater then``    ``// node value then recur down the tree``    ``if` `(key < node->key)``        ``node->left = insert(node->left, key);``    ``else` `if` `(key > node->key)``        ``node->right = insert(node->right, key);`` ` `    ``// return the (unchanged) node pointer``    ``return` `node;``}`` ` `// Returns largest value smaller than or equal to``// key. If key is smaller than the smallest, it ``// returns -1.``int` `findFloor(Node* root, ``int` `key)``{``    ``Node *curr = root, *ans = NULL;``    ``while` `(curr) {``        ``if` `(curr->key <= key) {``            ``ans = curr;``            ``curr = curr->right;``        ``}``        ``else``            ``curr = curr->left;``    ``}``    ``if` `(ans)``        ``return` `ans->key;``    ``return` `-1;``}`` ` `// Driver code``int` `main()``{``    ``int` `N = 25;`` ` `    ``Node* root = insert(root, 19);``    ``insert(root, 2);``    ``insert(root, 1);``    ``insert(root, 3);``    ``insert(root, 12);``    ``insert(root, 9);``    ``insert(root, 21);``    ``insert(root, 19);``    ``insert(root, 25);`` ` `    ``printf``(``"%d"``, findFloor(root, N));`` ` `    ``return` `0;``}`

## Java

 `// Java code to find the largest value smaller ``// than or equal to N ``class` `GFG``{``     ` `static` `class` `Node``{ ``    ``int` `key; ``    ``Node left, right; ``}; `` ` `// To create new BST Node ``static` `Node newNode(``int` `item) ``{ ``    ``Node temp = ``new` `Node(); ``    ``temp.key = item; ``    ``temp.left = temp.right = ``null``; ``    ``return` `temp; ``} `` ` `// To insert a new node in BST ``static` `Node insert(Node node, ``int` `key) ``{ ``    ``// if tree is empty return new node ``    ``if` `(node == ``null``) ``        ``return` `newNode(key); `` ` `    ``// if key is less then or grater then ``    ``// node value then recur down the tree ``    ``if` `(key < node.key) ``        ``node.left = insert(node.left, key); ``    ``else` `if` `(key > node.key) ``        ``node.right = insert(node.right, key); `` ` `    ``// return the (unchanged) node pointer ``    ``return` `node; ``} `` ` `// Returns largest value smaller than or equal to ``// key. If key is smaller than the smallest, it ``// returns -1. ``static` `int` `findFloor(Node root, ``int` `key) ``{ ``    ``Node curr = root, ans = ``null``; ``    ``while` `(curr != ``null``) ``    ``{ ``        ``if` `(curr.key <= key)``        ``{ ``            ``ans = curr; ``            ``curr = curr.right; ``        ``} ``        ``else``            ``curr = curr.left; ``    ``} ``    ``if` `(ans != ``null``) ``        ``return` `ans.key; ``    ``return` `-``1``; ``} `` ` `// Driver code ``public` `static` `void` `main(String[] args) ``{``    ``int` `N = ``25``; `` ` `    ``Node root = ``new` `Node();``    ``insert(root, ``19``); ``    ``insert(root, ``2``); ``    ``insert(root, ``1``); ``    ``insert(root, ``3``); ``    ``insert(root, ``12``); ``    ``insert(root, ``9``); ``    ``insert(root, ``21``); ``    ``insert(root, ``19``); ``    ``insert(root, ``25``); `` ` `    ``System.out.printf(``"%d"``, findFloor(root, N)); ``}``}`` ` `/* This code is contributed by PrinciRaj1992 */`

## Python3

 `# Python3 code to find the largest value ``# smaller than or equal to N`` ` `class` `newNode:``     ` `    ``def` `__init__(``self``, item):``         ` `        ``self``.key ``=` `item``        ``self``.left ``=` `None``        ``self``.right ``=` `None`` ` `# To insert a new node in BST``def` `insert(node, key):``     ` `    ``# If tree is empty return new node``    ``if` `(node ``=``=` `None``):``        ``return` `newNode(key)`` ` `    ``# If key is less then or grater then``    ``# node value then recur down the tree``    ``if` `(key < node.key):``        ``node.left ``=` `insert(node.left, key)``    ``elif` `(key > node.key):``        ``node.right ``=` `insert(node.right, key)`` ` `    ``# Return the (unchanged) node pointer``    ``return` `node`` ` `# Returns largest value smaller than or ``# equal to key. If key is smaller than``# the smallest, it returns -1.``def` `findFloor(root, key):``     ` `    ``curr ``=` `root``    ``ans ``=` `None``     ` `    ``while` `(curr):``        ``if` `(curr.key <``=` `key):``            ``ans ``=` `curr``            ``curr ``=` `curr.right``        ``else``:``            ``curr ``=` `curr.left``    ``if` `(ans):``        ``return` `ans.key``         ` `    ``return` `-``1`` ` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``     ` `    ``N ``=` `25``    ``root ``=` `None`` ` `    ``root ``=` `insert(root, ``19``)``    ``insert(root, ``2``)``    ``insert(root, ``1``)``    ``insert(root, ``3``)``    ``insert(root, ``12``)``    ``insert(root, ``9``)``    ``insert(root, ``21``)``    ``insert(root, ``19``)``    ``insert(root, ``25``)`` ` `    ``print``(findFloor(root, N))`` ` `# This code is contributed by bgangwar59`

## C#

 `// C# code to find the largest value smaller ``// than or equal to N ``using` `System;``using` `System.Collections.Generic; ``     ` `class` `GFG``{``     ` `public` `class` `Node``{ ``    ``public` `int` `key; ``    ``public` `Node left, right; ``}; `` ` `// To create new BST Node ``static` `Node newNode(``int` `item) ``{ ``    ``Node temp = ``new` `Node(); ``    ``temp.key = item; ``    ``temp.left = temp.right = ``null``; ``    ``return` `temp; ``} `` ` `// To insert a new node in BST ``static` `Node insert(Node node, ``int` `key) ``{ ``    ``// if tree is empty return new node ``    ``if` `(node == ``null``) ``        ``return` `newNode(key); `` ` `    ``// if key is less then or grater then ``    ``// node value then recur down the tree ``    ``if` `(key < node.key) ``        ``node.left = insert(node.left, key); ``    ``else` `if` `(key > node.key) ``        ``node.right = insert(node.right, key); `` ` `    ``// return the (unchanged) node pointer ``    ``return` `node; ``} `` ` `// Returns largest value smaller than or equal to ``// key. If key is smaller than the smallest, it ``// returns -1. ``static` `int` `findFloor(Node root, ``int` `key) ``{ ``    ``Node curr = root, ans = ``null``; ``    ``while` `(curr != ``null``) ``    ``{ ``        ``if` `(curr.key <= key)``        ``{ ``            ``ans = curr; ``            ``curr = curr.right; ``        ``} ``        ``else``            ``curr = curr.left; ``    ``} ``    ``if` `(ans != ``null``) ``        ``return` `ans.key; ``    ``return` `-1; ``} `` ` `// Driver code ``public` `static` `void` `Main(String[] args) ``{``    ``int` `N = 25; `` ` `    ``Node root = ``new` `Node();``    ``insert(root, 19); ``    ``insert(root, 2); ``    ``insert(root, 1); ``    ``insert(root, 3); ``    ``insert(root, 12); ``    ``insert(root, 9); ``    ``insert(root, 21); ``    ``insert(root, 19); ``    ``insert(root, 25); `` ` `    ``Console.Write(``"{0}"``, findFloor(root, N)); ``}``}`` ` `// This code is contributed by Rajput-Ji`

Output:

```25
```

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