617-merge-two-binary-trees.md

617. Merge Two Binary Trees - 合并二叉树

给定两个二叉树，想象当你将它们中的一个覆盖到另一个上时，两个二叉树的一些节点便会重叠。

你需要将他们合并为一个新的二叉树。合并的规则是如果两个节点重叠，那么将他们的值相加作为节点合并后的新值，否则不为 NULL 的节点将直接作为新二叉树的节点。

示例 1:

输入: 
	Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
输出: 
合并后的树:
	     3
	    / \
	   4   5
	  / \   \ 
	 5   4   7

注意: 合并必须从两个树的根节点开始。

---

题目标签：Tree

题目链接：LeetCode / LeetCode中国

题解

Language	Runtime	Memory
python3	152 ms	N/A

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

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
        else:
            if t1 is None:
                res = TreeNode(t2.val)
                res.left = self.mergeTrees(None, t2.left)
                res.right = self.mergeTrees(None, t2.right)
            elif t2 is None:
                res = TreeNode(t1.val)
                res.left = self.mergeTrees(t1.left, None)
                res.right = self.mergeTrees(t1.right, None)
            else:
                res = TreeNode(t1.val + t2.val)
                res.left = self.mergeTrees(t1.left, t2.left)
                res.right = self.mergeTrees(t1.right, t2.right)
            return res