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

#include <cstdio>
#include <cstring>
#include <algorithm>

const int maxm = 10000 + 500;
const int inf = 0x7fffffff >> 1;
int dp[maxm];
int n, m;
int x;

int main () {
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= m; i++) dp[i] = inf;
    dp[0] = 1;
    for (int i = 1; i <= n; i++) {
        scanf("%d", &x);
        for (int j = m; j >= x; j--) {
            if (dp[j - x] == inf) continue;
            if (dp[j] == inf) dp[j] = dp[j-x];
            else dp[j] += dp[j-x];
        }
    }
    if (dp[m] == inf) printf("0");
    else printf("%d", dp[m]);
    return 0;
}