原文题目:
Given two binary trees, write a function to check if they are equal or not.
Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
读题:
给定两个二叉树,判断二叉树是否相等,判断条件是二叉树的结构一样并且各个节点的value也一样
解题思路:
有两个方法,递归和非递归,递归是采用DFS方法遍历二叉树,对每个节点和左右子树进行判断;非递归方法可以采用栈或者队列存储两棵树进行逐一比较
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
'''递归'''
class Solution(object):
def isSameTree(self, p, q):
"""
:type p: TreeNode
:type q: TreeNode
:rtype: bool
"""
if p and q:
mid = p.val == q.val
l = self.isSameTree(p.left, q.left)
r = self.isSameTree(p.right, q.right)
return mid and l and r
return p == q
'''非递归'''
class Solution(object):
def isSameTree(self, p, q):
"""
:type p: TreeNode
:type q: TreeNode
:rtype: bool
"""
stack = [(p, q)]
while stack:
p, q = stack.pop()
if not p and not q:
continue
if not p or not q:
return False
if p.val == q.val:
stack.append((p.right, q.right))
stack.append((p.left, q.left))
else:
return False
return True