Two Sum BSTs

给两个bst, 然后看是不是能做two sum.

先用inorder变成array, 然后做two sum.

/**
 * 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 twoSumBSTs(TreeNode* root1, TreeNode* root2, int target) {
        vector<int> v; 
        inorder(root1, v); 
        return twosum(v, root2, target);
    }
    void inorder(TreeNode* root, vector<int>& v){
        if(!root)
            return;
        inorder(root->left, v);
        v.push_back(root->val);
        inorder(root->right, v);
    } 
    bool twosum(vector<int>& v, TreeNode* root, int t) {
        if(!root)
            return false;
        return binary_search(v.begin(), v.end(), t - root->val) || twosum(v, root->left, t) || twosum(v, root->right, t);;
    }
};