Merge Two Binary Trees问题及解法

问题描述：

Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not.

You need to merge them into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of new tree.

示例：

Input: Tree 1                     Tree 2                            1                         2                                      / \                       / \                                    3   2                     1   3                               /                           \   \                            5                             4   7                  Output: Merged tree:     3    / \   4   5  / \   \  5   4   7

问题分析：

采用深度递归遍历，将两数结合起来。

过程详见代码：

/** * 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;dfs(t1, t2);return t1;}void dfs(TreeNode* t1, TreeNode* t2){t1->val += t2->val;if (t1->left == NULL){t1->left = t2->left;}else if (t1->left != NULL && t2->left != NULL)dfs(t1->left, t2->left);if (t1->right == NULL){t1->right = t2->right;}else if (t1->right != NULL && t2->right != NULL)dfs(t1->right, t2->right);}};