Problem:
Score : 300 points

Problem Statement

There are N people numbered 1 to N. Each of them is either an honest person whose testimonies are always correct or an unkind person whose testimonies may be correct or not.

Person i gives A_i testimonies. The j-th testimony by Person i is represented by two integers x_{ij} and y_{ij}. If y_{ij} = 1, the testimony says Person x_{ij} is honest; if y_{ij} = 0, it says Person x_{ij} is unkind.

How many honest persons can be among those N people at most?

Constraints

All values in input are integers.

1 \leq N \leq 15

0 \leq A_i \leq N - 1

1 \leq x_{ij} \leq N

x_{ij} \neq i

x_{ij_1} \neq x_{ij_2} (j_1 \neq j_2)

y_{ij} = 0, 1

Input

Input is given from Standard Input in the following format:

N
A_1
x_{11} y_{11}
x_{12} y_{12}
:
x_{1A_1} y_{1A_1}
A_2
x_{21} y_{21}
x_{22} y_{22}
:
x_{2A_2} y_{2A_2}
:
A_N
x_{N1} y_{N1}
x_{N2} y_{N2}
:
x_{NA_N} y_{NA_N}

Output

Print the maximum possible number of honest persons among the N people.

Sample Input 1

3
1
2 1
1
1 1
1
2 0

Sample Output 1

2

If Person 1 and Person 2 are honest and Person 3 is unkind, we have two honest persons without inconsistencies, which is the maximum possible number of honest persons.

Sample Input 2

3
2
2 1
3 0
2
3 1
1 0
2
1 1
2 0

Sample Output 2

0

Assuming that one or more of them are honest immediately leads to a contradiction.

Sample Input 3

2
1
2 0
1
1 0

Sample Output 3

1

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static void Main(string[] args)
    {
        int N = int.Parse(Console.ReadLine());
        int[,] x = new int[N, N];
        int[,] y = new int[N, N];
        for (int i = 0; i < N; i++)
        {
            int num = int.Parse(Console.ReadLine());
            for(int j = 0; j < num; j++)
            {
                string[] input = Console.ReadLine().Split();
                x[i,j] = int.Parse(input[0]);
                y[i, j] = int.Parse(input[1]);
            }
        }
        int[] temp = new int[N];
        for (int i = 0; i < N; i++)
        {
            temp[i] = 0;
        }
        int ans = 0;
        for (int loop = 0; loop < Math.Pow(2, N); loop++)
        {
            bool flag = true;
            for (int i = 0; i < N; i++)
            {
                for (int j = 0; j < N; j++)
                {
                    if (temp[i] == 1)
                    {
                        if (x[i,j]!=0&&temp[x[i, j] - 1] != y[i, j]) { flag = false; }
                    }
                }
            }
            if (flag == true) { ans = Math.Max(ans,temp.Sum() ); }
            temp[0] += 1;
            for (int i = 0; i < N; i++)
            {
                if (i != N - 1 && temp[i] == 2) { temp[i + 1] += 1; temp[i] = 0; }
            }
        }
        Console.WriteLine(ans);
    }
}