acdream 1726 A Math game (部分和问题 DFS剪枝)

10 87
2 3 4 5 7 9 10 11 12 13
10 38
2 3 4 5 7 9 10 11 12 13

No
Yes

#include <cstdio>
#include <cstring>
#define ll long long
ll a[45], h, sum[45];
int n;
bool flag;
 
void DFS(ll num, int pos)
{
    if(num == h)
    {
        flag = true;
        return;
    }
    if(flag || pos == n + 1)  
        return;
    //若当前数字加剩下的数字和小于h或者当前数字大于h则返回
    //不加妥T
    if(sum[n] - sum[pos - 1] + num < h || num > h) 
        return;
    DFS(num + a[pos], pos + 1);
    DFS(num, pos + 1);
    return;
}
 
int main()
{
    while(scanf("%d %lld", &n, &h) != EOF)
    {
        memset(sum, 0, sizeof(sum));
        flag = false;
        for(int i = 1; i <= n; i++)
        {
            scanf("%lld", &a[i]);
            sum[i] = sum[i - 1] + a[i];
        }
        DFS(0, 1);
        if(flag)
            printf("Yes\n");
        else
            printf("No\n");
    }
}