solvable.dart

void main() {
  List<int> board = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];
  isSolvable(board) ? print("Solvable") : print("Not Solvable");
}

int getInvCount(List<int> arr){
  int inv_count = 0;
  int N = arr.length;
  for(int i = 0; i < N -1; i++){
    for (int j = i +(i * 4) + 1; j < N; j++){
      if (arr[j] && arr[i] && arr[i] > arr[j])
        inv_count++;
    }
  }
  return inv_count;
}

int findXPosition(List<int> arr) {
  int N = arr.length;
  for(int i = N-1; i >= 0; i--)
    for(int j = N-1; j>=0; j--)
      if(arr[i+(j * 4)] == 0)
        return N - i;
}

bool isSolvable(List<int> puzzle){
  int N = puzzle.length;
  int inv_count = getInvCount(puzzle);
  if(N & 1)
    return !(inv_count & 1);
  else {
    int pos = findXPosition(puzzle);
    if(pos & 1)
      return !(inv_count & 1);
    else
      return inv_count & 1;
  }
}

/*
     screen full of errors

hello.dart:13:14: Error: A value of type 'int' can't be assigned to a variable of type 'bool'.
Try changing the type of the left hand side, or casting the right hand side to 'bool'.
      if (arr[j] && arr[i] && arr[i] > arr[j])
             ^
hello.dart:13:24: Error: A value of type 'int' can't be assigned to a variable of type 'bool'.
Try changing the type of the left hand side, or casting the right hand side to 'bool'.
      if (arr[j] && arr[i] && arr[i] > arr[j])
                       ^
hello.dart:31:8: Error: A value of type 'int' can't be assigned to a variable of type 'bool'.
Try changing the type of the left hand side, or casting the right hand side to 'bool'.
  if(N & 1)
       ^
hello.dart:32:24: Error: A value of type 'int' can't be assigned to a variable of type 'bool'.
Try changing the type of the left hand side, or casting the right hand side to 'bool'.
    return !(inv_count & 1);
                       ^
hello.dart:35:12: Error: A value of type 'int' can't be assigned to a variable of type 'bool'.
Try changing the type of the left hand side, or casting the right hand side to 'bool'.
    if(pos & 1)
           ^
hello.dart:36:26: Error: A value of type 'int' can't be assigned to a variable of type 'bool'.
Try changing the type of the left hand side, or casting the right hand side to 'bool'.
      return !(inv_count & 1);
                         ^
hello.dart:38:24: Error: A value of type 'int' can't be assigned to a variable of type 'bool'.
Try changing the type of the left hand side, or casting the right hand side to 'bool'.
      return inv_count & 1;
                       ^
*/