[SCOI2008] bonus levels solution to a problem

Compare it routine

Since the optimal strategy to use, difficult to think backwards,

That is expected to generate a positive return after the election, the election is not negative returns.

I confidently presented, then immediately wrote the above sentence and then lost WA (my dishes ah). The correct one should be:

That is, after the election expected to produce larger returns than not vote on the election, otherwise not vote.

DP can then be a conventional pressure-like.

#include<iostream>
#include<cstdio>
using namespace std;

const int maxn = 105;
double dp[maxn][(1<<15)+5], ans;
int n, able[maxn], w[maxn], k;

void do_it(int x) {
    int i, j, t;
    for(i=0; i <= (1<<n)-1; i++) {
        for(j=1; j <= n; j++) {
            if((able[j] & i) == able[j]) {
                dp[x][i]+=max(dp[x+1][i], (dp[x+1][(i|(1<<j-1))]+w[j]))/(double)n;
            }
            else dp[x][i]+=dp[x+1][i]/(double)n;
        }
        //cout<<x<<' '<<i<<' '<<dp[x][i]<<endl;
    }
    return;
}

int main() {
    ios::sync_with_stdio(false);
    int i, t;
    cin>>k>>n;
    for(i=1; i <= n;i ++ ) {
        development>>w[i]>>t;
        while(t != 0) {
            able[i]=(able[i]|(1<<t-1));
            cin>>t;
        }
    }
    
    for(i=k; i >= 1; i--) do_it(i);
    printf("%.6lf", dp[1][0]);
    return 0;
}