【LeetCode】617. 合併兩個二叉樹

問題描述

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.

假設有兩棵二叉樹，假設你用其中一棵樹覆蓋另一棵樹，兩棵樹的一些節點是重疊的，而另一些不是。
你需要將它們合併到一個新的二叉樹中。合併規則是，如果兩個節點重疊，則將節點值相加作爲合併節點的新值。否則，不爲 null的節點將被用作新樹的節點。

輸入: 
	Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
輸出: 
合併後的新樹:
	     3
	    / \
	   4   5
	  / \   \ 
	 5   4   7

Python 實現

# 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 == None:
            return t2
        elif t2 == None:
            return t1 
        else:
            tNode = TreeNode(t1.val + t2.val)
            tNode.left = self.mergeTrees(t1.left, t2.left)
            tNode.right = self.mergeTrees(t1.right, t2.right)
            return tNode         

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