Leetcode题解-617. Merge Two Binary Trees

Leetcode题解-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.

思路

这根遍历一棵二叉树的思路是一样的，这里用先序遍历的方法。需要注意的小细节就是t1、t2是否为空以及传给左右子树的t1、t2分别该是什么

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