微信头像九宫格算法

public static List<ImageCell> (int n, int totalWidth) {
      int totalRow = (int) Math.ceil(Math.sqrt(n));
      int outline = 5;
      int width = ((totalWidth - outline) / totalRow);
      int border = width / 20;
      if (n == 1) {
          return Lists.newArrayList(new ImageCell(border, border, width - 2 * border));
      }
      int lastAloneNum = n % totalRow;
      int totalFullRow = n / totalRow;
      int lastRow = totalRow - totalFullRow - 1;
      int firstStartX = (totalWidth - lastAloneNum * width) / 2;
      int firstStartY = lastRow * width;
      int otherSpace = (totalWidth - totalRow * width) / 2;
      int yOffset = 0;
      if (totalRow != totalFullRow + (lastAloneNum != 0 ? 1 : 0)) {
          yOffset = -width / 2;
      }
      List<ImageCell> imageCells = Lists.newArrayList();
      for (int i = 0; i < n; i++) {
          int x = 0, y = firstStartY;
          if (i < lastAloneNum) {
              x = firstStartX + i * width;
          } else {
              x = (i - lastAloneNum) % totalRow * width;
              y = firstStartY + ((i - lastAloneNum) / totalRow + 1) * width;
          }
          imageCells.add(new ImageCell(x + border + otherSpace, y + border + otherSpace + yOffset, width - 2 * border));
      }
      return imageCells;
  }
  
  @AllArgsConstructor
  static class ImageCell {
      int x;
      int y;
      int width;
  }