101. 对称二叉树

原题

https://leetcode.cn/problems/symmetric-tree/description/

思路

递归

复杂度

时间：O(n)
空间：O(n)

Python代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        def isMirror(node1, node2):
            if not node1 and not node2:
                return True 
            if not node1 or not node2:
                return False 
            if node1.val != node2.val:
                return False
            return isMirror(node1.left, node2.right) and isMirror(node1.right, node2.left)

        return isMirror(root.left, root.right)
        

Go代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isSymmetric(root *TreeNode) bool {
	// 匿名函数
	var isMirror func(*TreeNode, *TreeNode) bool
	isMirror = func(node1 *TreeNode, node2 *TreeNode) bool {
		if node1 == nil && node2 == nil {
			return true
		}
		if node1 == nil || node2 == nil {
			return false
		}
		if node1.Val != node2.Val {
			return false
		}
		return isMirror(node1.Left, node2.Right) && isMirror(node1.Right, node2.Left)

	}

	return isMirror(root.Left, root.Right)
}