653.txt

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
/**
 * 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 <int> a; 
        mid_order(root,a);
        int left=0;
        int right=a.size()-1;
        while (left<right){
            if (a[left]+a[right]==k) return true;
            if (a[left]+a[right]<k)   left++;
            if (a[left]+a[right]>k)   right--;
            
            
            
        }
        
      return false;
        
  
        
    }
    
    
    
private:
    void mid_order(TreeNode* root, vector<int>&a){
        if(root==nullptr) return ;
        
        mid_order(root->left, a);
        a.push_back(root->val);
        mid_order(root->right, a);
            
    
    }
    
};