59. 螺旋矩阵 II 中等

问题：

给你一个正整数 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 n x n 正方形矩阵 matrix 。

示例 1：

输入：n = 3
输出：[[1,2,3],[8,9,4],[7,6,5]]

示例 2：

输入：n = 1
输出：[[1]]

回答：

var generateMatrix = function(n) {
    let res = new Array(n).fill().map(() => {
        return new Array(n).fill(0)
    });
    let left = 0;
    let top = 0;
    let right = n - 1;
    let bottom = n - 1;
    let cur = 1;  
    while (top <= bottom && left <= right) {
        for (let i = left; i <= right; i++) {
            res[top][i] = cur;
            cur = cur + 1;
        }
        top++;
        for (let i = top; i <= bottom; i++) {
            res[i][right] = cur;
            cur = cur + 1;
        }
        right--;
        if (top <= bottom) {
            for (let i = right; i >= left; i--) {
                res[bottom][i] = cur;
                cur = cur + 1;
            }
        }
        bottom--;
        if (left <= right) {
            for (let i = bottom; i >= top; i--) {
                res[i][left] = cur;
                cur = cur + 1;
            }
        }
        left++;
    }
    return res;
};