Zoj 3640 Help Me Escape (expected)

Zoj 3640 Help Me Escape (expected)

 

 

This question is terrible.

A vampire is trapped and has n ways to escape. Each road has a difficulty c []. His initial combat power is f. For the I-th Road, if f> c [I], he will spend t [I] days to go out. Otherwise, he will stay for one day, increase the fighting capacity of c [I], and then select another way to go out, the probability of each route is the same. Ask him about the days he expected to escape.

If dp [I] is set to indicate the expected value of escaping when the combat capability is I, the state equation can be introduced.

Dp [I] = 1/n * t [j] (c [j]> I ), dp [I] = 1/n * (1 + dp [I + c [j]) (c [j] <= I ).

Note that the final State is determined. When f> Max, the expected value is the average value of the total time, But I + c [j] may be greater than Max + 1, so the final state should be Max * 2. During initialization, you forget to multiply by 2.

In addition, t [I] is an integer.

 

 

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             #include //#define LL __int64#define LL long long#define eps 1e-8#define PI acos(-1.0)using namespace std;const int INF = 0x3f3f3f3f;const int maxn = 4010;double dp[10010];int c[110];double t[110];int main(){int n,f;int Max;double sum_t,ave_t;while(~scanf(%d %d,&n,&f)){Max = f;sum_t = 0;for(int i = 1; i <= n; i++){scanf(%d,&c[i]);t[i] = (int) ( (1+sqrt(5))*0.5*c[i]*c[i] );Max = max(Max,c[i]);sum_t += t[i];}ave_t = sum_t/n;if(f > Max){printf(%.3lf,ave_t);continue;}memset(dp,0,sizeof(dp));for(int i = Max+1; i <= 20000; i++)dp[i] = ave_t;for(int i = Max; i >= f; i--){for(int j = 1; j <= n; j++){if(i > c[j]){dp[i] += t[j];}else{dp[i] += 1+dp[i+c[j]];}}dp[i] /= n;}printf(%.3lf,dp[f]);}return 0;}