P4799 [CEOI2015 Day2]世界冰球锦标赛

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#include<bits/stdc++.h>
using namespace std;
#define int long long
const int MAXn = 40;

template <typename T>
inline void read(T &a) {
    char c;for (c = getchar(); (c < '0' || c > '9') && c != '-'; c = getchar());bool f = c == '-';T x = f ? 0 : (c ^ '0');for (c = getchar(); c >= '0' && c <= '9'; c = getchar()) {x = x * 10 + (c ^ '0');}a = f ? -x : x;
}
template <typename T, typename ...Argv>
inline void read(T &a, Argv &...argv) {
    read(a), read(argv...);
}

map<int, int> map1, map2;
int n, midn, W, w[MAXn + 10];
signed main() {
    read(n, W);
    midn = n >> 1;
    for (int i = 1; i <= n; ++i) {
        read(w[i]);
    }
    map1[0] = map2[0] = 1;
    for (int i = 1; i <= midn; ++i) {
        auto j = end(map1), bottomj = begin(map1);
        for (--j; ; --j) {
            map1[(*j).first + w[i]] += map1[(*j).first];
            if (j == bottomj) break;
        }
    }
    for (int i = midn + 1; i <= n; ++i) {
        auto j = end(map2), bottomj = begin(map2);
        for (--j; ; --j) {
            map2[(*j).first + w[i]] += map2[(*j).first];
            if (j == bottomj) break;
        }
    }
    int sum = 0, ans = 0;
    auto j = begin(map2), topj = end(map2);
    auto i = end(map1), bottomi = begin(map1);
    for (--i; ; --i) {
        int topmapj = W - (*i).first;
        while (j != topj && (*j).first <= topmapj) {
            sum += (*j).second;
            ++j;
        }
        ans += (*i).second * sum;
        if (i == bottomi) break;
    }
    printf("%lld\n", ans);
    return 0;
}