[leetcode]: 617. Merge Two Binary Trees

1.题目

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.
合并两棵二叉树，相同位置的节点的值相加作为新的二叉树的节点的值。
Example 1:
Input:

Tree 1                     Tree 2                        1                         2                                  / \                       / \                                3   2                     1   3                           /                           \   \                        5                             4   7                  

Output:
Merged tree:

     3    / \   4   5  / \   \  5   4   7

2.分析

同时遍历两棵二叉树，相同位置的节点值相加。
可以递归or迭代

3.代码

递归

TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {    if (t1 == NULL&&t2 == NULL)        return NULL;    else {        TreeNode* node = new TreeNode(0);        if (t1)            node->val += t1->val;        if (t2)            node->val += t2->val;        node->left = mergeTrees(t1 ? t1->left : NULL, t2 ? t2->left : NULL);        node->right = mergeTrees(t1 ? t1->right : NULL, t2 ? t2->right : NULL);        return node;    }}