findIndexByPosition static method

int findIndexByPosition(
  1. List<ChapterInfo>? chapters,
  2. int positionMs
)

根据播放位置查找当前章节索引（二分查找，O(log n)）

前提条件：chapters 必须按 startMs 升序排列，且章节区间连续不重叠。 如果传入未排序的列表，二分查找将返回错误结果。

Find chapter index by playback position using binary search (O(log n)). Prerequisite: chapters must be sorted by startMs in ascending order, and chapter intervals must be continuous and non-overlapping. Passing an unsorted list will produce incorrect results.

chapters 章节列表 positionMs 当前播放位置（毫秒） 返回当前章节索引，未找到返回 -1

Implementation

static int findIndexByPosition(List<ChapterInfo>? chapters, int positionMs) {
  if (chapters == null || chapters.isEmpty) return -1;

  int low = 0;
  int high = chapters.length - 1;

  while (low <= high) {
    final int mid = (low + high) >>> 1;
    final ChapterInfo chapter = chapters[mid];
    if (positionMs < chapter.startMs) {
      high = mid - 1;
    } else if (positionMs >= chapter.endMs) {
      low = mid + 1;
    } else {
      return mid;
    }
  }
  return -1;
}