[48] 旋转图像

/**
 * @param {number[][]} matrix
 * @return {void} Do not return anything, modify matrix in-place instead.
 */
var rotate = function (matrix) {
  const ll = matrix.length
  const remainder = ll % 2
  const level = (ll - remainder) / 2
  for (let y = 0; y < level; y++) {
    for (let x = y; x < ll - y - 1; x++) {
      const startingPoint = matrix[x][y]
      matrix[x][y] = matrix[ll - 1 - y][x]
      matrix[ll - 1 - y][x] = matrix[ll - 1 - x][ll - 1 - y]
      matrix[ll - 1 - x][ll - 1 - y] = matrix[y][ll - 1 - x]
      matrix[y][ll - 1 - x] = startingPoint
    }
  }
};