Symmetric Tree

题目介绍

LeetCode 101. Symmetric Tree。

复杂度

时间复杂度: O(n), 空间复杂度: O(n)

解题思路

public class TreeNode {
    public var val: Int
    public var left: TreeNode?
    public var right: TreeNode?
    public init(_ val: Int) {
        self.val = val
        self.left = nil
        self.right = nil
    }
}

class Solution {
    func isSymmetric(_ root: TreeNode?) -> Bool {
        return isMirror(root, root)
    }

    func isMirror(_ left: TreeNode?, _ right: TreeNode?) -> Bool {
        if left == nil && right == nil {
            return true
        }
        if left == nil || right == nil {
            return false
        }
        if left?.val != right?.val {
            return false
        }
        return isMirror(left?.right, right?.left) && isMirror(left?.left, right?.right)
    }
}

class Solution2 {
    func isSymmetric(_ root: TreeNode?) -> Bool {
        var queue: [TreeNode?] = []
        queue.append(root)
        queue.append(root)
        while !queue.isEmpty {
            let q = queue.removeFirst()
            let p = queue.removeFirst()
            if q == nil && p == nil {
                continue
            }
            if q == nil || p == nil {
                return false
            }
            if q!.val != p!.val {
                return false
            }
            queue.append(q!.left)
            queue.append(p!.right)
            queue.append(q!.right)
            queue.append(p!.left)
        }
        return true
    }
}

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