【51nod-1432】独木舟

排序后用二分，一直卡在最后一组数据，最后改成long long才AC...

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
vector<LL> a;
int main()
{
    LL n, m, sum = , x;
    cin>>n>>m;
    for(LL i=; i<n; i++)
    {
        scanf("%lld", &x);
        a.push_back(x);
    }
    sort(a.begin(), a.end());
    while(a.size() > )
    {
        LL x = a.back();
        LL s = m-x;
        a.erase(a.end()-);
        LL k = upper_bound(a.begin(), a.end(), s)-a.begin();
        if(a[k-]<=s)
        {
            a.erase(a.begin()+k-);
            sum++;
        }
        else
            sum++;
    }
    printf("%lld\n", a.size()==?sum+:sum);
    return ;
}