合并两个二叉树

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

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.

给定两个二叉树，将两棵树相同节点相加，不同节点保留

Example

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Input: 
4Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
Output: 
Merged tree:
4     3
4    / \
4   4   5
4  / \   \ 
4 5   4   7

Answer

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def mergeTrees(self, t1, t2):
        """
        :type t1: TreeNode
        :type t2: TreeNode
        :rtype: TreeNode
        """
        if t1 and t2:
            t = TreeNode(t1.val + t2.val)
            t.left = self.mergeTrees(t1.left, t2.left)
            t.right = self.mergeTrees(t1.right, t2.right)
            return t
        else:
            return t1 or t2

Thinging

递归