Problem:
Score : 300 points

Problem Statement

We have two permutations P and Q of size N (that is, P and Q are both rearrangements of (1,~2,~...,~N)).

There are N! possible permutations of size N. Among them, let P and Q be the a-th and b-th lexicographically smallest permutations, respectively. Find |a - b|.

Notes

For two sequences X and Y, X is said to be lexicographically smaller than Y if and only if there exists an integer k such that X_i = Y_i~(1 \leq i < k) and X_k < Y_k.

Constraints

2 \leq N \leq 8

P and Q are permutations of size N.

Input

Input is given from Standard Input in the following format:

N
P_1 P_2 ... P_N
Q_1 Q_2 ... Q_N

Output

Print |a - b|.

Sample Input 1

3
1 3 2
3 1 2

Sample Output 1

3

There are 6 permutations of size 3: (1,~2,~3), (1,~3,~2), (2,~1,~3), (2,~3,~1), (3,~1,~2), and (3,~2,~1). Among them, (1,~3,~2) and (3,~1,~2) come 2-nd and 5-th in lexicographical order, so the answer is |2 - 5| = 3.

Sample Input 2

8
7 3 5 4 2 1 6 8
3 8 2 5 4 6 7 1

Sample Output 2

17517

Sample Input 3

3
1 2 3
1 2 3

Sample Output 3

0

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define contains(v, t) (find(v.begin(), v.end(), t) != v.end())
#define MOD 1000000007
typedef long long ll;
typedef unsigned long long ull;

int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for(int i = 1; i <= n; i++) {
    a[i-1] = i;
  }

  vector<int> p(n), q(n);
  rep(i, n) {
    cin >> p[i];
  }
  rep(i, n) {
    cin >> q[i];
  }
  int ra, rb;
  int count = 1;
  do {
    bool pm = true;
    bool qm = true;
    rep(i, n) {
      if (p[i] != a[i]) pm = false;
      if (q[i] != a[i]) qm = false;
    }

    if (pm) ra = count;
    if (qm) rb = count;
    count++;
  } while (next_permutation(begin(a), end(a)));

  cout << abs(ra - rb);
}