The 2013 ACM-ICPC Asia Changsha Regional Contest J Josephina and RPG

Josephina and RPG

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Time Limit: 2 Seconds      Memory Limit: 65536 KB      Special Judge

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A role-playing game (RPG and sometimes roleplaying game) is a game in which players assume the roles of characters in a fictional setting. Players take responsibility for acting out these roles within a narrative, either through literal acting or through a process of structured decision-making or character development.

Recently, Josephina is busy playing a RPG named TX3. In this game, M characters are available to by selected by players. In the whole game, Josephina is most interested in the "Challenge Game" part.

The Challenge Game is a team play game. A challenger team is made up of three players, and the three characters used by players in the team are required to be different. At the beginning of the Challenge Game, the players can choose any characters combination as the start team. Then, they will fight with N AI teams one after another. There is a special rule in the Challenge Game: once the challenger team beat an AI team, they have a chance to change the current characters combination with the AI team. Anyway, the challenger team can insist on using the current team and ignore the exchange opportunity. Note that the players can only change the characters combination to the latest defeated AI team. The challenger team get victory only if they beat all the AI teams.

Josephina is good at statistics, and she writes a table to record the winning rate between all different character combinations. She wants to know the maximum winning probability if she always chooses best strategy in the game. Can you help her?

Input

There are multiple test cases. The first line of each test case is an integer M (3 ≤ M ≤ 10), which indicates the number of characters. The following is a matrix T whose size is R × R. R equals to C(M, 3). T(i, j) indicates the winning rate of team i when it is faced with team j. We guarantee that T(i, j) + T(j, i) = 1.0. All winning rates will retain two decimal places. An integer N (1 ≤ N≤ 10000) is given next, which indicates the number of AI teams. The following line contains N integers which are the IDs (0-based) of the AI teams. The IDs can be duplicated.

Output

For each test case, please output the maximum winning probability if Josephina uses the best strategy in the game. For each answer, an absolute error not more than 1e-6 is acceptable.

Sample Input

40.50 0.50 0.20 0.300.50 0.50 0.90 0.400.80 0.10 0.50 0.600.70 0.60 0.40 0.5030 1 2

Sample Output

0.378000

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Author: LIN, Yue
Contest: The 2013 ACM-ICPC Asia Changsha Regional Contest
Submit    Status

题意：就是告诉你C(m,3)个队伍相互之间的胜率，然后要你依次对战n个AI队伍，首先任选一种队伍，然后战胜一个AI后可以选择替换成AI的队伍，也可以不换，问你最后最大的胜率是多少。

这题主要是理解题意，然后就是简单的动态规划了。。

dp[i][j]代表是对战前i个队伍后且当前的队伍是j的最大胜率。。

dp[i][j] = max(dp[i][j],dp[i-1][j]*P[j][no[i]]); //代表不换
dp[i][no[i]] = max(dp[i][no[i]],dp[i-1][j]*P[j][no[i]]);//代表换战队

如果是在杭电上提交的要注意了，好像杭电上是没有特殊判断，所以要保留6位小数。。。

#include<cstdio>#include<cstring>double P[150][150];double dp[10005][325];int no[10005];int m,n;int C[] = {0,0,0,1,4,10,20,35,56,84,120};double max(double a,double b){return a>b?a:b;}int main(){int i,j;while(~scanf("%d",&m)){memset(dp,0,sizeof(dp));for(i=0;i<C[m];i++)for(j=0;j<C[m];j++)scanf("%lf",&P[i][j]);scanf("%d",&n);for(i=1;i<=n;i++)scanf("%d",&no[i]);for(i=0;i<=C[m];i++)dp[0][i] = 1;for(i=1;i<=n;i++)for(j=0;j<C[m];j++){dp[i][j] = max(dp[i][j],dp[i-1][j]*P[j][no[i]]);dp[i][no[i]] = max(dp[i][no[i]],dp[i-1][j]*P[j][no[i]]);}double ans = 0;for(i=0;i<C[m];i++)ans = max(dp[n][i],ans);printf("%0.7f\n",ans);}return 0;}