function vortex(n, m) {
  const nums = new Array(n).fill(0).map(() => new Array(m).fill(0))
  let i = 0 // 行号
  let j = 0 // 列号
  let stepI = 0 // 每次 i 增加的数字
  let stepJ = 1 // 每次 j 增加的数字
  let count = 1
  function hasBlock() {
    return !nums[i] || nums[i][j] !== 0
  }
  while (true) {
    nums[i][j] = count++
    i += stepI
    j += stepJ
    if (hasBlock()) {
      i -= stepI
      j -= stepJ
      if (stepI === 0) {
        stepI = stepJ
        stepJ = 0
      } else {
        stepJ = -stepI
        stepI = 0
      }
      i += stepI
      j += stepJ
      if (hasBlock()) {
        break
      }
    }
  }
  return nums
}