Leetcode 101. Symmetric Tree

原创于 2021-04-29 12:07:31 发布 · 115 阅读

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本文介绍了一种通过递归方法判断给定二叉树是否镜像自身的算法。通过比较左右子树的对称关系，代码展示了如何检查每层节点是否对称。适用于对数据结构和递归理解的应用开发者。

Problem

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Algorithm

Recursion. If a trees is mirror of itself, the left sub-tree’s left sub-tree is mirror of the right sub-tree’s right sub-tree and the left sub-tree’s right sub-tree is mirror of the right sub-tree’s left sub-tree.

Code

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        def isSymmetric(L, R):
            if L and R:
                if L.val == R.val:
                    return isSymmetric(L.left, R.right) and isSymmetric(L.right, R.left)
                else:
                    return False
            elif not L and not R:
                return True
            else:
                return False
        
        if root:
            return isSymmetric(root.left, root.right)
        return True