算法课程Leetcode作业第四周技术博客

题目：617. Merge Two Binary Trees

题目描述：

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.

Note: The merging process must start from the root nodes of both trees.

解题思路：

使用递归算法

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

递归算法的关键步骤在于如何结束递归（判断树指针为空时，返回另外的树指针，这样就不会继续执行下面调用mergeTrees（）的递归语句）