FXTi's blog
0%

merge-two-binary-trees

Posted on Edited on

Merge Two Binary Trees – LeetCode 617

Problem

Description

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.

Answer

Original

Code

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
/**
 * 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 && !t2)
            return nullptr;
        else if(t1 && t2){
            t1->val += t2->val;
            t1->left = mergeTrees(t1->left, t2->left);
            t1->right = mergeTrees(t1->right, t2->right);
            return t1;
        } else{
            return t1 ? t1 : t2;
        }
    }
};

思路

简单的利用t1树整合保存结果。时间复杂度$O(n)$，空间复杂度$O(1)$。
耗时$28$ ms，排名$14.80\%$

Better

思路

还没看到更好的思路