1935-买装备-backtracking,dp

 

#include <stdio.h>

long long s[20], x[20] = { 0 }, c,sum=0; int n;
//回溯法解决子集和问题 ，子集中的那个数若存在则记为1，否则为0
int backtrack(int t) {
    static int count=0;
    int i;
    if (t == n) {
        if (sum == c)
        {
            count++;
            return count;
        }
    }
    else
    {
        //去除掉第1,2,3，...个元素后满足的情况，选择分支1
        sum += s[t];
        x[t] = 1;
        backtrack(t + 1);
        //不去除时满足的情况，选择分支2
        x[t] = 0;
        sum -= s[t];
        backtrack(t + 1);
        return count;
    }

}
int main()
{
    int count=0;
    scanf("%d%lld", &n, &c);
    for (int i = 0; i < n; i++) {
        scanf("%lld", &s[i]);
        x[i] = 0;
    }
    count=backtrack(0);
    printf("%d", count);
    return 0;
}