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 Scala (2.11.7) (judge verdict: Accepted)

object Main extends App {
  val n = readInt
  val a = Array.fill(n)(0)
  val xy:Array[List[(Int,Int)]] = Array.fill(n)(Nil)
  for (i <- 0 until n) {
    a(i) = readInt
    (0 until a(i)).foreach{ _ =>
      xy(i) = (readLine.split(" ").map{_.toInt} match {case x => (x(0)-1,x(1))}) :: xy(i)
    }
  }
  
  def solve(i:Int,honestList:List[Int]):Int = {
    if (i == n) {
      val h = honestList.reverse.toArray
      val ok = (
        for (i <- 0 until n) yield {
          if (h(i)==1) xy(i).map{case (x,y) => h(x) == y}.forall{_ == true} else true
        }).forall{_ == true}
      if (ok) h.sum else 0
    }
    else {
      scala.math.max(solve(i+1,0::honestList),solve(i+1,1::honestList))
    }
  }
  
  println(solve(0,Nil))
}