Codeforces Gym 100338I TV Show DFS
2017-02-28 01:42
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题目链接:
http://codeforces.com/gym/100338/attachments题意:
一个人去参加电视有奖问答的节目,初始奖金为100元,每答对一道问题奖金翻倍,答错奖金清零。此外有一次保险机会:花费C的奖金,下一题可以答对奖金翻倍,答错奖金不清零。现在给你答对每道题的概率,求最优答题策略的奖金期望。
题解:
http://blog.csdn.net/qq_15714857/article/details/48035161枚举到第i题前离开 , 并且在第k题(k小于i)使用保险,注意k可以等于0,表示 不用
代码:
code 1:#include <bits/stdc++.h> using namespace std; typedef long long ll; #define MS(a) memset(a,0,sizeof(a)) #define MP make_pair #define PB push_back const int INF = 0x3f3f3f3f; const ll INFLL = 0x3f3f3f3f3f3f3f3fLL; inline ll read(){ ll x=0,f=1;char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} return x*f; } ////////////////////////////////////////////////////////////////////////// const int maxn = 1e5+10; double p[55],dp[55][55]; int n,c; double ans; // 做到第t题 在x题之前离开 在第k题用保险,得到sum元的概率是pp【 p[1]*p[2]*p[3]*... void dfs(int t,int x,int k,double sum,double pp){ if(t == x){ dp[x][k] += sum*pp; ans = max(ans,dp[x][k]); return ; }else if(sum>=c && k==t){ dfs(t+1,x,k,(sum-c),pp*(1-p[t])); dfs(t+1,x,k,(sum-c)*2,pp*p[t]); } else dfs(t+1,x,k,sum*2,pp*p[t]); } int main(){ freopen("tvshow.in","r",stdin); freopen("tvshow.out","w",stdout); n=read(),c=read(); for(int i=1; i<=n; i++){ cin >> p[i]; p[i] /= 100; } for(int i=1; i<=n+1; i++) for(int k=0; k<i; k++) // k=0 可以不用保险 dfs(1,i,k,100.0,1.0); printf("%.10lf\n",ans); return 0; } // http://codeforces.com/gym/100338/attachments[/code]
code 2:#include <bits/stdc++.h> using namespace std; typedef long long ll; #define MS(a) memset(a,0,sizeof(a)) #define MP make_pair #define PB push_back const int INF = 0x3f3f3f3f; const ll INFLL = 0x3f3f3f3f3f3f3f3fLL; inline ll read(){ ll x=0,f=1;char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} return x*f; } ////////////////////////////////////////////////////////////////////////// const int maxn = 1e5+10; int n,c; double p[55]; double dfs(int t,double sum,bool have){ if(t >= n){ return sum; } double tmp = max(sum,p[t]*dfs(t+1,sum*2,have)); double money = 0; if(sum>=c && have){ money += p[t] * dfs(t+1,(sum-c)*2,false); money += (1-p[t]) * dfs(t+1,(sum-c),false); } tmp = max(tmp,money); return tmp; } int main(){ freopen("tvshow.in","r",stdin); freopen("tvshow.out","w",stdout); cin >> n >> c; for(int i=0; i<n; i++){ cin >> p[i]; p[i] /= 100; } double ans = dfs(0,100.0,true); // true表示还有保险 printf("%.10lf\n",ans); return 0; } // http://codeforces.com/gym/100338/attachments[/code]
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