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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        Map<Integer, Set<Integer>[]> map = new HashMap<>();
        for(int i = 1; i <= n ; i++) {
        	map.put(i, new HashSet[2]);
        	map.get(i)[0] = new HashSet<>();
        	map.get(i)[1] = new HashSet<>();
        }

        for(int i = 1; i <= n; i++) {
        	int num = sc.nextInt();
        	for(int j = 0; j < num; j++) {
        		int people = sc.nextInt();
        		int flag = sc.nextInt();
        		if(flag == 1) 
        		    map.get(i)[0].add(people);
        		else
        		    map.get(i)[1].add(people);
        	}
        }
        int ans = 0;
        Set<Integer> trueSets = new HashSet<>();
        Set<Integer> falseSets = new HashSet<>();
        loop:
        for(int bit = 0; bit < (1 << n); bit++) {
        	trueSets = new HashSet<>();
        	falseSets = new HashSet<>();
        	for(int j = 0; j < n; j++) {
        	    int p = j + 1;
        		if((bit >> j & 1) == 1) {
        			trueSets.addAll(map.get(p)[0]);
        			falseSets.addAll(map.get(p)[1]);
        		}
        	}

        	for(int j = 0; j < n; j++) {
        	    int p = j + 1;
        		if((bit >> j & 1) == 1) {
        			if(falseSets.contains(p))
        				continue loop;
        		} else {
        		    if(trueSets.contains(p))
        				continue loop;
        		}
        	}
        	if(trueSets.size() != Integer.bitCount(bit))
        	    continue loop;

        	ans = Math.max(ans, Integer.bitCount(bit));
        }

        System.out.println(ans);
    }
}