12.LeetCode刷题For Swift·59. Spiral Matrix II螺旋矩阵II

1、原题

给定一个正整数 n，生成一个包含 1 到 n2 所有元素，且元素按顺时针顺序螺旋排列的正方形矩阵。

示例:

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

2、思路

理解了这个题的逻辑，方法就很简单了，主要还是确定上下左右边界，一条边一条边填充。

3、代码

class Solution {
    func generateMatrix(_ n: Int) -> [[Int]] {
        // 定义上下左右边界，
        var top = 0
        var right = n - 1
        var bottom = n - 1
        var left = 0
        // 返回结果
        var result = [[Int]](repeating: [Int](repeating: 0, count: n), count:n)
        // 初始值从1开始
        var num = 1
        // 结束值
        let target = n * n
        while num <= target {
            // 从左到右从上倒下开始排列
            for i in stride(from: left, through: right, by: 1) {
                result[top][i] = num
                num += 1
            }
            // 排完一列，内缩
            top += 1
            for i in stride(from: top, through: bottom, by: 1) {
                result[i][right] = num
                num += 1
            }
            right -= 1
            for i in stride(from: right, through: left, by: -1) {
                result[bottom][i] = num
                num += 1
            }
            bottom -= 1
            for i in stride(from: bottom, through: top, by: -1) {
                result[i][left] = num
                num += 1
            }
            left += 1
        }
        return result
    }
}