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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
)

func main() {
	var n int
	fmt.Scan(&n)
	sl := make([]map[int]int, n)

	for i := 0; i < n; i++ {
		var a int
		fmt.Scan(&a)
		sl[i] = map[int]int{}
		for j := 0; j < a; j++ {
			var x, y int
			fmt.Scan(&x, &y)
			sl[i][x-1] = y
		}
	}

	var max int
	for bit := 0; bit < (1 << uint(n)); bit++ {
		ok := true
		for i := 0; i < n; i++ {
			if (bit>>uint(i))&1 == 1 {
				for k, v := range sl[i] {
					if v != ((bit >> uint(k)) & 1) {
						ok = false
						break
					}
				}
			}
		}
		if ok {
			cnt := onesCount(bit)
			if cnt > max {
				max = cnt
			}
		}
	}
	fmt.Println(max)
}

func onesCount(bit int) int {
	var num int
	for ; bit != 0; bit &= bit - 1 {
		num++
	}
	return num
}