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.Collections.Generic;
using System;

public class P
{
    public int x { get; set; }
    public int y { get; set; }
}

public class Hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        var a = new List<P>[n];
        for (int i = 0; i < n; i++)
        {
            var c = int.Parse(Console.ReadLine().Trim());
            a[i] = new List<P>();
            for (int j = 0; j < c; j++)
            {
                string[] line = Console.ReadLine().Trim().Split(' ');
                var t1 = int.Parse(line[0]) - 1;
                var t2 = int.Parse(line[1]);
                a[i].Add(new P { x = t1, y = t2 });
            }
        }
        getAns(n, a);
    }
    static void getAns(int n, List<P>[] a)
    {
        var ans = 0;
        var imax = 1 << n;
        for (int i = 0; i < imax; i++)
        {
            var cb = countBit(i);
            if (cb > ans && check(n, a, i)) ans = cb;
        }
        Console.WriteLine(ans);
    }
    static bool check(int n, List<P>[] a, int i)
    {
        for (int j = 0; j < n; j++)
            if (((i >> j) & 1) == 1)
                foreach (var x in a[j])
                    if (((i >> x.x) & 1) != x.y) return false;
        return true;
    }
    static int countBit(int bits)
    {
        bits = (bits & 0x55555555) + (bits >> 1 & 0x55555555);
        bits = (bits & 0x33333333) + (bits >> 2 & 0x33333333);
        bits = (bits & 0x0f0f0f0f) + (bits >> 4 & 0x0f0f0f0f);
        bits = (bits & 0x00ff00ff) + (bits >> 8 & 0x00ff00ff);
        return (bits & 0x0000ffff) + (bits >> 16 & 0x0000ffff);
    }
}