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 =  + ;

 int t;

 int n,l;

 int a[maxn];

 int b[maxn];

 int flag[maxn];

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