LeetCode 617. Merge Two Binary Trees（归并两棵二叉树）

题意：归并两棵二叉树。

/**
 * 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:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if(t1 == NULL) return t2;
        if(t2 == NULL) return t1;
        t1 -> val += t2 -> val;
        t1 -> left = mergeTrees(t1 -> left, t2 -> left);
        t1 -> right = mergeTrees(t1 -> right, t2 -> right);
        return t1;
    }
};