有哪些学习算法的网站推荐？

输入：matrix = [[1,2,3],[4,5,6],[7,8,9]]
输出：[1,2,3,6,9,8,7,4,5]

输入：matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
输出：[1,2,3,4,8,12,11,10,9,5,6,7]

class SpiralMatrix {
    func spiralOrder(_ matrix: [[Int]]) -> [Int] {
        var res = [Int]()

        guard matrix.count != 0 else {
            return res
        }

        var startX = 0
        var endX = matrix.count - 1
        var startY = 0
        var endY = matrix[0].count - 1

        while true {
            // top
            for i in startY...endY {
                res.append(matrix[startX][I])
            }
            startX += 1
            if startX > endX {
                break
            }

            // right
            for i in startX...endX {
                res.append(matrix[i][endY])
            }
            endY -= 1
            if startY > endY {
                break
            }

            // bottom
            for i in stride(from: endY, through: startY, by: -1) {
                res.append(matrix[endX][I])
            }
            endX -= 1
            if startX > endX {
                break
            }

            // left
            for i in stride(from: endX, through: startX, by: -1) {
                res.append(matrix[i][startY])
            }
            startY += 1
            if startY > endY {
                break
            }
        }

        return res
    }
}