881. 救生艇 2021-08-26

class Solution {
public:
    int numRescueBoats(vector<int>& people, int limit) {
        sort(people.begin(), people.end());
        int count = 0;
        vector<bool> used(people.size(), false);
        for (int i = (int) people.size() - 1; i >= 0; --i) {
            if (used[i])
                continue;
            ++count;
            auto pt = upper_bound(people.begin(), people.begin() + i, limit - people[i]);
            if (pt == people.begin())
                continue;
            do {
                --pt;
                if (!used[pt - people.begin()]) {
                    used[pt - people.begin()] = true;
                    break;
                }
            } while (pt != people.begin());
        }
        return count;
    }
};