[LeetCode] Challenge log 617

Posted on | Edited on |
617. Merge Two BInary Trees

https://leetcode.com/problems/merge-two-binary-trees/description/

DFS Problem. Recursive Solution.

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:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
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.

Soulution:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
class Solution:
    def mergeTrees(self, t1, t2):
        """
        :type t1: TreeNode
        :type t2: TreeNode
        :rtype: TreeNode
        """
        if t1 is None and t2 is None: 
            return None
        elif t1 is None:
            return t2
        elif t2 is None:
            return t1
        else:
            t1.val += t2.val
            t1.left = self.mergeTrees(t1.left, t2.left)
            t1.right = self.mergeTrees(t1.right, t2.right)
            return t1
0%