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
如果二叉搜索树中存在2个数之和等于目标值，则返回true
C++（33ms）：
/**
* 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_set<int> Set ;
return dfs(root, k , Set) ;
}
bool dfs(TreeNode* root, int k , unordered_set<int>& Set) {
if (root == NULL)
return false ;
if (Set.count(k - root->val))
return true ;
Set.insert(root->val) ;
return dfs(root->left,k,Set) || dfs(root->right,k,Set) ;
}
};
653. Two Sum IV - Input is a BST
原文：http://www.cnblogs.com/mengchunchen/p/7994370.html