POJ 3071 Football

Football

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 2366		Accepted: 1191

Description

Consider a single-elimination football tournament involving 2ⁿ teams, denoted 1, 2, …, 2ⁿ. In each round of the tournament, all teams still in the tournament are placed in a list in order of increasing index. Then, the first team in the list plays the second team, the third team plays the fourth team, etc. The winners of these matches advance to the next round, and the losers are eliminated. After n rounds, only one team remains undefeated; this team is declared the winner.

Given a matrix P = [p_ij] such that p_ij is the probability that team i will beat team j in a match determine which team is most likely to win the tournament.

Input

The input test file will contain multiple test cases. Each test case will begin with a single line containing n (1 ≤ n ≤ 7). The next 2ⁿ lines each contain 2ⁿ values; here, the jth value on the ith line represents p_ij. The matrix P will satisfy the constraints that p_ij = 1.0 − p_ji for all i ≠ j, and p_ii = 0.0 for all i. The end-of-file is denoted by a single line containing the number −1. Note that each of the matrix entries in this problem is given as a floating-point value. To avoid precision problems, make sure that you use either the double data type instead of float.

Output

The output file should contain a single line for each test case indicating the number of the team most likely to win. To prevent floating-point precision issues, it is guaranteed that the difference in win probability for the top two teams will be at least 0.01.

Sample Input

2
0.0 0.1 0.2 0.3
0.9 0.0 0.4 0.5
0.8 0.6 0.0 0.6
0.7 0.5 0.4 0.0
-1

Sample Output

2
题目大意：输入n，总共有2^n支球队，每支球队战胜其他球队的概率通过矩阵输入，求夺冠概率最大的球队是哪支球队。
解题方法：概率DP。

#include <stdio.h>
#include <iostream>
#include <string.h>
using namespace std;

int main()
{
    double p[200][200];
    double dp[200][200];//dp[i][j]代表第i轮比赛中j胜出的概率
    int n;
    while(scanf("%d", &n) != EOF && n != -1)
    {
        memset(dp, 0, sizeof(dp));
        for (int i = 0; i < 1 << n; i++)
        {
            for (int j = 0; j < 1 << n; j++)
            {
                scanf("%lf", &p[i][j]);
            }
        }
        for (int i = 0; i < 1 << n; i++)
        {
            dp[0][i] = 1;
        }
        for (int i = 1; i <= n; i++)//总共有n轮比赛
        {
            for (int j = 0; j < (1 << n); j++)
            {
                int t = j / (1 << (i - 1));
                t ^= 1;
                for (int k = t * (1 << (i - 1)); k < t * (1 << (i - 1)) + (1 << (i - 1)); k++)
                {
                    dp[i][j] += dp[i - 1][j] * dp[i - 1][k] * p[j][k];
                }
            }
        }
        double temp = 0.0;
        int ans;
        for (int i = 0; i < 1 << n; i++)
        {
            if (dp[n][i] > temp)
            {
                temp = dp[n][i];
                ans = i;
            }
        }
        printf("%d\n", ans + 1);
    }
    return 0;
}