The Solution to Leetcode 617 Merge Two Binary Trees

Question:

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

思路：
合并两个二叉树，就是在对应的节点位置上进行值相加，为空的节点按值为零处理。

用递归方法可以求出合并的二叉树。

Answer:

/**
* 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)
return t2;
if (t2==NULL)
return t1;
t1->val=t1->val+t2->val;

t1->left = mergeTrees(t1->left,t2->left);
t1->right = mergeTrees(t1->right,t2->right);
return t1;
}
};

Run code result:


Your input

[1,3,2,5]
[2,1,3,null,4,null,7]

Your answer

[3,4,5,5,4,null,7]

Expected answer

[3,4,5,5,4,null,7]