[54] 螺旋矩阵

/**
 * @param {number[][]} matrix
 * @return {number[]}
 */
var spiralOrder = function (matrix) {
  const m = matrix.length
  const n = matrix[0].length
  const ans = []
  let left = 0, top = 0, right = n - 1, bottom = m - 1

  while (left <= right && top <= bottom) {
    for (let i = left; i <= right; i++) ans.push(matrix[top][i])
    if (++top > bottom) break;
    for (let i = top; i <= bottom; i++) ans.push(matrix[i][right])
    if (--right < left) break;
    for (let i = right; i >= left; i--) ans.push(matrix[bottom][i])
    if (bottom-- < top) break;
    for (let i = bottom; i >= top; i--) ans.push(matrix[i][left])
    if (++left > right) break;

  }
  return ans
};