Uva1149

每个bin最多只能放两个，所以最佳的贪心策略是从大的开始放，如果有空间放第二个，尽量放最大的。

#include <bits/stdc++.h>

using namespace std;

const int maxn = 100000 + 10;

int t;

int n,l;

int a[maxn];

int b[maxn];

int flag[maxn];

void solve(){
    int cnt = 0;
    memset(flag, 0, sizeof(flag));
    for(int i = 1; i <= n; ++i){
            if(flag[i]){
                continue;
            } else {
                ++cnt;
                flag[i] = 1;
                int temp = l - a[i];
                int loc = upper_bound(b+1, b+1+n, temp) - b;
                if(loc == 1+n) loc = n;
                for(int j = loc; j >= 1; --j){
                    if(!flag[n-j+1] && b[j] <= temp){
                        flag[n-j+1] = 1;
                        break;
                    }
                }
            }
    }
    printf("%d\n",cnt);
    if(t) printf("\n");
}

bool cmp(int a, int b){
    return a > b;
}

int main(){
        scanf("%d",&t);
        while(t--){
            scanf("%d%d",&n,&l);
            for(int i = 1; i <= n; ++i){
                scanf("%d",&a[i]);
                b[i] = a[i];
            }
            if(l == 0){
                printf("0\n");
                continue;
            }
            sort(a+1, a+1+n, cmp);
            sort(b+1, b+1+n);
            solve();
        }
}