[59] 螺旋矩阵 II

/**
 * @param {number} n
 * @return {number[][]}
 */
var generateMatrix = function (n) {
  const matrix = Array.from(Array(n), () => Array(n).fill(0));
  let left = 0, top = 0, right = n - 1, bottom = n - 1
  let number = 0;
  while (left <= right && top <= bottom) {
    for (let i = left; i <= right; i++) matrix[top][i] = ++number
    if (++top > bottom) break;
    for (let i = top; i <= bottom; i++) matrix[i][right] = ++number
    if (--right < left) break;
    for (let i = right; i >= left; i--) matrix[bottom][i] = ++number
    if (bottom-- < top) break;
    for (let i = bottom; i >= top; i--)matrix[i][left] = ++number
    if (++left > right) break;
  }
  return matrix
};