100. Same Tree Leetcode Python

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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

这道题目考察的是树的比较和遍历。可以采用任何一种遍历方式，只要能保证比较到树中的所有节点.只要有任何一个节点不符合条件就返回false

这里采用Preorder的方法。

We need to traverse the whole tree and compare every value of the two trees. If any of the value is not the same return False

# Definition for a  binary tree node# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution:    # @param p, a tree node    # @param q, a tree node    # @return a boolean    def isSameTree(self, p, q):        if q==None and p==None:            return True        if q and p and p.val==q.val:           return self.isSameTree(p.left,q.left) and self.isSameTree(p.right,q.right)        return False

这里用非recursive的方法解决，主要思想是用两个stack来maintain node

# Definition for a  binary tree node# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution:    # @param p, a tree node    # @param q, a tree node    # @return a boolean    def isSameTree(self, p, q):        if p==None and q==None:            return True        if p==None and q!=None:            return False        if p!=None and q==None:            return False        stack1=[p]        stack2=[q]        while stack1 and stack2:            n1=stack1.pop()            n2=stack2.pop()            if n1.val==n2.val:                if n1.left:                    stack1.append(n1.left)                if n2.left:                    stack2.append(n2.left)                if len(stack1)!=len(stack2):                    return False                if n1.right:                    stack1.append(n1.right)                if n2.right:                    stack2.append(n2.right)                if len(stack1)!=len(stack2):                    return False            else:                return False                        return True

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