100. Same Tree

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