力扣--59.螺旋矩阵II

模拟顺时针画矩阵的过程:

• 填充上行从左到右
• 填充右列从上到下
• 填充下行从右到左
• 填充左列从下到上

由外向内一圈一圈这么画下去

/**
 * 生成一个包含从1到n*n的数字的矩阵
 * @param {number} n - 矩阵的大小，为正整数
 * @return {number[][]} - 返回一个n x n的二维数组，数组中的每个元素为从1到n*n的递增数字
 */
var generateMatrix = function (n) {
let matrix = new Array(n);
    for (let i = 0; i < n; i++) {
        matrix[i] = new Array(n).fill(0);
    }

    let top = 0, bottom = n - 1, left = 0, right = n - 1;
    let direction = [[-1, 0], [0, 1], [1, 0], [0, -1]]; // 上、右、下、左四个方向
    let index = 0;

    while (top <= bottom && left <= right) {
        // 沿着当前方向遍历边界
        for (let i = left; i <= right; i++) {
            matrix[top][i] = ++index;
        }
        top++;

        for (let i = top; i <= bottom; i++) {
            matrix[i][right] = ++index;
        }
        right--;

        if (top <= bottom) {
            for (let i = right; i >= left; i--) {
                matrix[bottom][i] = ++index;
            }
            bottom--;
        }

        if (left <= right) {
            for (let i = bottom; i >= top; i--) {
                matrix[i][left] = ++index;
            }
            left++;
        }
    }

    return matrix;
};