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.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass
{
	public const long Giri = 1000000007;
	public class Person
	{
		public long[] Says {get;set;}
		public Person(long k )
		{
			Says = new long[k];
		}
	}
	public static void Main(string[] args)
	{
		int n = (int)Console.ReadLine().ToLong();
		Person[] people = new Person[n];
		
		for(long i = 0; i < n; i++)
		{
			var a = Console.ReadLine().ToLong();
			people[i] = new Person(n);
			
			for(long j = 0; j < a; j++)
			{
				var p = Input().ToInt();
				people[i].Says[p[0]-1] = p[1]+1;
			}
		}
		long max = 0;
		for(long bit = 0; bit < (1 << n); bit++)
		{
			bool mujun = false;
			long cnt = 0;
			for(int i = 0; i < n; i++)
			{
				long h = ((bit >> i) & 1);
				if(h == 1)
					cnt++;
				//Console.Write(h);
				var says = people[i].Says;
				
				for(int k = 0; k < says.Length; k++)
				{
					if(k == i || says[k] == 0)
						continue;
					int q = -1;
					if((h == 1 && says[k] == 2))// || (h == 0 && says[k] == 1))
					{
						q = 1;	//syouzikimono
					}
					if((h == 1 && says[k] == 1))// || (h == 0 && says[k] == 2))
					{
						q = 0;	//tigau
						//Console.WriteLine("SET>>{3},{2};{0}={1}", k, says[k], bit, h);
					}
					//Console.WriteLine("{0}={1}",q, ((bit >> k) & 1));
					if(q == -1)
						continue;
					if(((bit >> k) & 1) == q)
					{
					}
					else
					{
						mujun = true;
						break;
					}
				}
				if(mujun)	break;
			
			}
			if(!mujun)
			{
				max = Math.Max(max, cnt);
			}
		}
		Console.WriteLine(Math.Min(n, max));
	}

	static long GCD(long a, long b)
	{
		var v = new[] { a, b };
		while (v[1] != 0) { v = new[] { v[1], v[0] % v[1] }; }
		return v[0];
	}
	public static string[] Input() { return Console.ReadLine().Split(' '); }
	public static long Clamp(int val, int max, int min = 0) { return Math.Min(max, Math.Max(min, val)); }
}

public static class Smarter
{
	public static int ToInt(this string str) { return int.Parse(str); }
	public static long ToLong(this string str) { return long.Parse(str); }
	public static int[] ToInt(this string[] str)
	{
		var r = new int[str.Length];
		for(int i = 0; i < str.Length; i++) r[i] = str[i].ToInt();
		return r;
	 }
}