LeetCode---617. Merge Two Binary Trees

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.

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

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

大意为：

输入2个二叉树，输出计算他们合并后的二叉树（原谅我的英文一般都不咋地，简洁几句话就好）

解题思路：

想到树的问题，一般都会想怎么去遍历，递归或者非递归，本人使用的是递归方式；然后思考递归中怎么合并同个位置的值，如果存在一个有值一个为空的又如何处理

附上代码

  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;    }