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。
 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 const int maxn = 100000 + 10;
 6 
 7 int t;
 8 
 9 int n,l;
10 
11 int a[maxn];
12 
13 int b[maxn];
14 
15 int flag[maxn];
16 
17 void solve(){
18     int cnt = 0;
19     memset(flag, 0, sizeof(flag));
20     for(int i = 1; i <= n; ++i){
21             if(flag[i]){
22                 continue;
23             } else {
24                 ++cnt;
25                 flag[i] = 1;
26                 int temp = l - a[i];
27                 int loc = upper_bound(b+1, b+1+n, temp) - b;
28                 if(loc == 1+n) loc = n;
29                 for(int j = loc; j >= 1; --j){
30                     if(!flag[n-j+1] && b[j] <= temp){
31                         flag[n-j+1] = 1;
32                         break;
33                     }
34                 }
35             }
36     }
37     printf("%d
",cnt);
38     if(t) printf("
");
39 }
40 
41 bool cmp(int a, int b){
42     return a > b;
43 }
44 
45 int main(){
46         scanf("%d",&t);
47         while(t--){
48             scanf("%d%d",&n,&l);
49             for(int i = 1; i <= n; ++i){
50                 scanf("%d",&a[i]);
51                 b[i] = a[i];
52             }
53             if(l == 0){
54                 printf("0
");
55                 continue;
56             }
57             sort(a+1, a+1+n, cmp);
58             sort(b+1, b+1+n);
59             solve();
60         }
61 }