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Two Sum IV - Input is a BST

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Description

https://leetcode.com/problems/two-sum-iv-input-is-a-bst/

Solution

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool findTarget(TreeNode* root, int k) {
        unordered_map<int, int> mapping;
        if (root == NULL || (root->left ==NULL && root->right == NULL)) return false;
        bool ret = false;
        helper(mapping, root, k, ret);
        return ret;
    }
    
    void helper(unordered_map<int, int>& mapping, TreeNode* root, int k, bool& ret) {
        if (ret || root == NULL) return;
        if (mapping.count(k - root->val) != 0) {ret = true; return;}
        mapping[root->val] = 1;
        helper(mapping, root->right, k, ret);
        helper(mapping, root->left, k , ret);
        return;
    }
};