【Leetcode】617. Merge Two Binary Trees

cheney康

于 2018-03-28 22:39:28 发布

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本文链接：https://blog.youkuaiyun.com/cheneykl/article/details/79735465

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本文介绍了一种将两棵二叉树合并成一棵新二叉树的算法。当两棵树的节点重叠时，新树的节点值为两树相应节点值之和；若节点不重叠，则采用非空节点作为新树的节点。文中通过示例详细解释了该算法的工作原理。

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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.

class Solution:
    def mergeTrees(self, t1, t2):
        
        if not t1:
            return t2
        elif not t2:
            return t1
        root = TreeNode(t1.val+t2.val)
        root.left = self.mergeTrees(t1.left, t2.left)
        root.right = self.mergeTrees(t1.right , t2.right)
        return root