Two Sum IV - Input is a BST

Description

Given the root of a binary search tree and an integer k, return true if there exist two elements in the BST such that their sum is equal to k, or false otherwise.

Example 1:

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

Example 2:

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

Constraints:

• The number of nodes in the tree is in the range [1, 104].
• -104 <= Node.val <= 104
• root is guaranteed to be a valid binary search tree.
• -105 <= k <= 105

Code

/**
 * 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:
    bool findTarget(TreeNode* root, int k) {
        set<int> m;
        return helper(root, m, k);
    }
 
    bool helper(TreeNode* node, set<int>& map, int target) {
        if(!node) return false;
        if(map.count(target - node->val) > 0) return true;
        map.insert(node->val);
        return helper(node->left, map, target) || helper(node->right, map, target);
    }
};

Source

• Two Sum IV - Input is a BST - LeetCode