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 Kotlin (1.0.0) (judge verdict: Accepted)

data class Testify(val x: Int, val y: Boolean)
fun main(args: Array<String>) {
    val N = nextInt()
    val A = Array(N) { mutableListOf<Testify>() }
    repeat(N) {
        val a = it
        val n = nextInt()
        repeat(n) {
            val (x, y) = listOfInt()
            A[a].add(Testify(x - 1, y == 1))
        }
    }
    var ans = 0
    var bit = 0
    while (bit < (1 shl N)) {
        val v = BooleanArray(N)
        for (b in 0 until N) {
            v[b] = (bit and (1 shl b)) != 0
        }
        var ok = true
        for (n in 0 until N) {
            if (!v[n]) continue //★
            for (t in A[n]) {
                if (v[t.x] xor t.y) ok = false
            }
        }
        if (ok) ans = Math.max(ans, v.count { it })
        bit += 1
    }
    println(ans)
}
fun next() = readLine()!!
fun nextInt() = Integer.parseInt(next())
fun listOfString() = next().split(" ")
fun listOfInt(delta: Int = 0) = listOfString().map { Integer.parseInt(it) + delta }
fun printErr(value: Any) = System.err.println(value)