leetcode 617. Merge Two Binary Trees (Python)

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

Code

# 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 not t1 and not t2:
            return None
        elif t1 == None:
            return t2
        elif t2 == None:
            return t1
        else:
            root = TreeNode(t1.val+t2.val)
            root.left = self.mergeTrees(t1.left,t2.left)
            root.right = self.mergeTrees(t1.right, t2.right)
        return  root
        

method2：

# 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 not t1 and not t2:
            return None
        root = TreeNode((t1.val if t1 else 0)+(t2.val if t2 else 0))
        root.left = self.mergeTrees(t1 and t1.left, t2 and t2.left)
        root.right = self.mergeTrees(t1 and t1.right, t2 and t2.right)
        return  root