100. Same Tree

100. Same Tree

1 题目

1. Given two binary trees, write a function to check if they are the same or not.

   Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

   Example 1:

   Input:     1         1
             / \       / \
            2   3     2   3
   
           [1,2,3],   [1,2,3]
   
   Output: true
   

   Example 2:

   Input:     1         1
             /           \
            2             2
   
           [1,2],     [1,null,2]
   
   Output: false
   

   Example 3:

   Input:     1         1
             / \       / \
            2   1     1   2
   
           [1,2,1],   [1,1,2]
   
   Output: false
   

2 解题 && 思路

对2棵树分别做前序遍历，然后把前序的字符串比较。注意左右子树是空，需要特殊标记。

3. 实现

# 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 dlr(self,tree,dirlist):
        if tree is None :
            return 
        if tree.left is not None :
            self.dlr(tree.left,dirlist)
        else:
            dirlist.append(-2)
        dirlist.append(tree.val)
        if tree.right is not None :
            self.dlr(tree.right,dirlist)
        else:
            dirlist.append(-1)
        
    
    def isSameTree(self, p, q):
        """
        :type p: TreeNode
        :type q: TreeNode
        :rtype: bool
        """
        p_list = []
        q_list = []

        self.dlr(p,p_list)
        self.dlr(q,q_list)
        p_str=""
        q_str=""
        for e in p_list:
            p_str = p_str+str(e)
        for e in q_list:
            q_str = q_str+str(e)
 
        return p_str == q_str