[LeetCode] 101. Symmetric Tree( 与 100 对应)

题：https://leetcode.com/problems/symmetric-tree/description/

题目

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
1
/ \
2 2
/ \ / \
3 4 4 3
But the following [1,2,2,null,3,null,3] is not:
1
/ \
2 2
\ \
3 3

思路

和对比 same tree 的思路一样，将一棵树视为 root.left 与 root.right树，看两树是否对称。
具体步骤，在递归时 对比两树的 左子树，与右子树。

Code

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
def isPartSym(p,q):
    if p == None and q == None:
        return True
    if p == None or q == None:
        return False
    if p.val == q.val:
        return isPartSym(p.left,q.right) and isPartSym(p.right,q.left)
    return False


class Solution:
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root ==None:
            return True
        return isPartSym(root.left,root.right)