算法 - 插入排序交换次数 - Binary Indexed Tree

• 场景：快速得到一段数组元素的和
• 题目：Insertion Sort Advanced Analysis | HackerRank
• 算法：binary-indexed-tree :: HackerRank
• 实现：binary-indexed-tree :: HackerRank 已经给出基本的实现了

// get cumulative sum up to and including i
int Get(int i) {
  int res = 0;
  while(i) {
    res += B[i];
    i -= (i & -i);
  }
  return res;
}

// add val to value at i
void Set(int i, int val) {
  while(i <= N) {
    B[i] += val;
    i += (i & -i);
  }
}