leetcode 101 对称二叉树

题目 给定一个二叉树，检查它是否是镜像对称的。

方法一 递归:

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def isSymmetric(self, root: TreeNode) -> bool:

        def isMirror(node1, node2):
            if node1 is None and node2 is None:
                return True
            elif node1 is None or node2 is None:
                return False
            else:
                if node1.val != node2.val:
                    return False
                else:
                    return isMirror(node1.left, node2.right) and isMirror(node1.right, node2.left)
            
        return isMirror(root, root)

使用递归, 速度有点慢

方法二: 迭代

使用列表存储从每个节点交叉遍历的结果,看每相邻的两个是否相同:

def isSymmetric(self, root: TreeNode) -> bool:
        li = []
        li.append(root)
        li.append(root)
        while len(li) != 0:
            node1 = li.pop()
            node2 = li.pop()
            if node1 is None and node2 is None:
                pass
            elif node1 is None or node2 is None:
                return False
            elif node1.val != node2.val:
                return False
            else:
                li.append(node1.left)
                li.append(node2.right)

                li.append(node1.right)
                li.append(node2.left)
        return True

结果如下,更慢了