小A点菜 水题 dp 背包

基本上还是01背包，首先注意必须正好花光钱，所以初始化时除了dp[0]以外其他都要设置成inf，然后因为求方案数，所以基本方程为dp[i] = dp[i-x] + dp[i]，再根据inf进行一些特殊处理即得解

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4
 5 const int maxm = 10000 + 500;
 6 const int inf = 0x7fffffff >> 1;
 7 int dp[maxm];
 8 int n, m;
 9 int x;
10
11 int main () {
12     scanf("%d %d", &n, &m);
13     for (int i = 1; i <= m; i++) dp[i] = inf;
14     dp[0] = 1;
15     for (int i = 1; i <= n; i++) {
16         scanf("%d", &x);
17         for (int j = m; j >= x; j--) {
18             if (dp[j - x] == inf) continue;
19             if (dp[j] == inf) dp[j] = dp[j-x];
20             else dp[j] += dp[j-x];
21         }
22     }
23     if (dp[m] == inf) printf("0");
24     else printf("%d", dp[m]);
25     return 0;
26 }