Given a Binary Search Tree and a target number, return true if there exist two elements in the BST such that their sum is equal to the given target.
Example 1:
Input: 5 / \ 3 6 / \ \ 2 4 7 Target = 9 Output: True
Example 2:
Input: 5 / \ 3 6 / \ \ 2 4 7 Target = 28 Output: False
A:
/** * 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) { unordered_set<int> S; return helper(S, root, k); } private: bool helper(unordered_set<int> &S, TreeNode* root, int k) { if(root == nullptr){ return false; } if(S.find(k-root->val) != S.end()) return true; S.insert(root->val); return helper(S, root->left, k) || helper(S, root->right, k); } };
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