主要思路
我们先来考虑无限制的版本,也就是不考虑询问的硬币数量限制。我们可以用一个完全背包搞一搞,复杂度为线性。
dp[0] = 1; for (int i = 0; i < 4; i++) for (int j = ci[i]; j < MAX_N; j++) dp[j] += dp[j - ci[i]];
那么我们如何做到复杂度小的询问呢?我们可以考虑容斥原理,把答案搞成:
\[ dp[s] – dp[s-(d_{1}+1)*c_{1}] – dp[s-(d_{2}+1)*c_{2}] – dp[s-(d_{3}+1)*c_{3}] – dp[s-(d_{4}+1)*c_{4}] + dp[s-(d_{1}+1)*c_{1}-(d_{2}+1)*c_{2}] + dp[s-(d_{1}+1)*c_{1}-(d_{3}+1)*c_{3}] + dp[s-(d_{1}+1)*c_{1}-(d_{4}+1)*c_{4}] \dots \]
然后用二进制搞个容斥就行了:
// P1450.cpp #include <bits/stdc++.h> #define ll long long using namespace std; const int MAX_N = 101000; int ci[5], tot, di[5], si; ll dp[101000]; int main() { for (int i = 0; i < 4; i++) scanf("%d", &ci[i]); dp[0] = 1; for (int i = 0; i < 4; i++) for (int j = ci[i]; j < MAX_N; j++) dp[j] += dp[j - ci[i]]; scanf("%d", &tot); while (tot--) { for (int j = 0; j < 4; j++) scanf("%d", &di[j]); scanf("%d", &si); ll ans = 0; for (int i = 0; i < 16; i++) { ll C = si, T = 0; for (int j = 0; j < 4; j++) if ((i >> j) & 1) C -= (di[j] + 1) * ci[j], T ^= 1; if (C < 0) continue; ans += (T ? -1 : 1) * dp[C]; } printf("%lld\n", ans); } return 0; }