C++ブラシLeetcode 653.両数の和IV

                ，   BST                      ，    true。

   1:

  : 
    5
   / \
  3   6
 / \   \
2   4   7

Target = 9

  : True
 

   2:

  : 
    5
   / \
  3   6
 / \   \
2   4   7

Target = 28

  : False

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

/**
 * 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) {
        vector ivec;
        if(!root)
            return false;
        TreeNode *p = root;
        stack s;
        while(!s.empty() || p)
        {
            while(p)
            {
                s.push(p);
                p = p -> left;
            }
            if(!s.empty())
            {
                ivec.push_back(s.top() -> val);
                p = s.top() -> right;
                s.pop();
            }
        }
        unordered_map hash;
        for(int i = 0; i != ivec.size(); ++i)
        {
            if(hash.count(k - ivec[i]))
                return true;
            hash[ivec[i]] = i;
        }
        return false;
    }
};