# Two Sum IV - Input Is A BST Problem

## Description

LeetCode Problem 653.

Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.

Example 1:

``````1
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Input: root = [5,3,6,2,4,null,7], k = 9
Output: true
``````

Example 2:

``````1
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Input: root = [5,3,6,2,4,null,7], k = 28
Output: false
``````

Example 3:

``````1
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Input: root = [2,1,3], k = 4
Output: true
``````

Example 4:

``````1
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Input: root = [2,1,3], k = 1
Output: false
``````

Example 5:

``````1
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Input: root = [2,1,3], k = 3
Output: true
``````

Constraints:

• The number of nodes in the tree is in the range [1, 10^4].
• -10^4<= Node.val <= 10^4
• root is guaranteed to be a valid binary search tree.
• -10^5<= k <= 10^5

## Sample C++ Code

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/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode() : val(0), left(nullptr), right(nullptr) {}
*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
map<int, int> m;
bool findTarget(TreeNode* root, int k) {
if (root == NULL)
return false;
if (m.find(k-root->val) != m.end()) {
return true;
}
m[root->val] = 1;
return findTarget(root->left, k) || findTarget(root->right, k);
}
};
``````