超大01背包问题（二分）

 #include
 #include
 #include
 using namespace std;
 const int N = 50;
 const long long INF = 0x3fffffff;
 typedef long long LL;
 int n;
 LL w[N], v[N];
 LL W;
 pair  pi[1 << (N / 2)];

 void solve() {
     int n2 = n / 2;
     for(int i = 0; i < (1 << n2); i++) {
         LL sw = 0, sv = 0;
         for(int j = 0; j < n2; j++) {
             if((i >> j) & 1) {
                 sw += w[j];
                 sv += v[j];
             }
         }
         pi[i] = make_pair(sw, sv);
     }

     sort(pi, pi + (1 << n2));
     int m = 1;
     for(int i = 1; i < (1 << n2); i++) {
         if(pi[m-1].second < pi[i].second) {
             pi[m++] = pi[i];
         }
     }

     LL res = 0;
     for(int i = 0; i < (1 << (n - n2)); i++) {
         LL sw = 0, sv = 0;
         for(int j = 0; j < n - n2; j++) {
             if((i >> j) & 1) {
                 sw += w[n2 + j];
                 sv += v[n2 + j];
             }
         }
         if(sw <= W) {
             LL tv = (lower_bound(pi, pi + m, make_pair(W - sw, INF)) - 1)->second;
             res = max(res, sv + tv);
         }
     }
     printf("%lld\n", res);
 }

 int main() {
     while(~scanf("%d%lld", &n, &W)) {
         for(int i = 0; i < n; i++) {
             scanf("%lld%lld", &w[i], &v[i]);
         }
         solve();
     }
     return 0;
 }