性能优化

struct Item {
  ......
  int calcWight();
}
bool comp(Item a, Item b)
{
    return a.calcWeight() < b.calcWeight();
}
std::stable_sort(items.begin(), items.end(), comp);

struct Score
{
      int score;
      int idx;
}
int n = items.size();
for (int i = 0; i < n; ++i)
{
    scores[i].score = items[i].calcWeight();
    scores.idx = i;
}
bool comp(Score a, Score b)
{
    return a.score < b.score;
}
stable_sort(scores, scores + n, comp);
......