Problem:
Score : 200 points

Problem Statement

You are given a string S of length N.
Among its subsequences, count the ones such that all characters are different, modulo 10^9+7. Two subsequences are considered different if their characters come from different positions in the string, even if they are the same as strings.

Here, a subsequence of a string is a concatenation of one or more characters from the string without changing the order.

Constraints

1 \leq N \leq 100000

S consists of lowercase English letters.

|S|=N

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of the subsequences such that all characters are different, modulo 10^9+7.

Sample Input 1

4
abcd

Sample Output 1

15

Since all characters in S itself are different, all its subsequences satisfy the condition.

Sample Input 2

3
baa

Sample Output 2

5

The answer is five: b, two occurrences of a, two occurrences of ba. Note that we do not count baa, since it contains two as.

Sample Input 3

5
abcab

Sample Output 3

17

Solution in C++ (GCC 9.2.1) (judge verdict: Wrong Answer)



#include <bits/stdc++.h>
#include <string.h>
#include <vector>
//s#define rep(i, n) for (int i = 0; i < (n); i++)
#define MAX 10000

using namespace std;

#define ll long long
#define pb push_back
#define mp make_pair
#define all(a) (a).begin(),(a).end()
#define rep(i,a,n) for(int i=a; i<n; i++)
#define r0 return 0
#define INF (int)1e15
#define MOD 1000000007

#define access(i) a[i/3][i%3]
int gcd(int x, int y)
{
    if(y==0)
        return x;
    return gcd(y, x%y);
}

 long long numbers[500005];

  int main(){

  string s;
  cin>>s;
  long long k;
  cin>>k;

  long long cnt = 0,n = s.length();

  for(int i=0;i<n-1;i++){

   if(s[i] == s[i+1]){
    cnt++;
    i++; }
  }

  cout<<cnt*k<<endl;

  return 0;
  }