59. 螺旋矩阵 II

执行用时：0 ms, 在所有 Swift 提交中击败了100.00% 的用户
内存消耗：13.5 MB, 在所有 Swift 提交中击败了69.44% 的用户

class Solution {
    func generateMatrix(_ n: Int) -> [[Int]] {
        var matrix = [[Int]].init(repeating: [Int].init(repeating: 0, count: n), count: n)
        var left = 0, right = n - 1, top = 0, bottom = n - 1
        var num = 1
        while left <= right && top <= bottom {
            for col in left ... right {
                matrix[top][col] = num
                num += 1
            }
            if (top + 1 <= bottom) {
                for row in (top+1) ... bottom {
                    matrix[row][right] = num
                    num += 1
                }
            }
 
            if left < right && top < bottom {
                for col in stride(from: right-1, to: left, by: -1) {
                    matrix[bottom][col] = num
                    num += 1
                }
                
                for row in stride(from: bottom, to: top, by: -1) {
                    matrix[row][left] = num
                    num += 1
                }
            }
            left += 1
            right -= 1
            top += 1
            bottom -= 1
        }
        return matrix
    }
}