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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(signed i=0;i<n;++i)
#define repi(n) rep(i,n)
#define int long long
#define str string
#define vint vector<int>
#define pint pair<int,int>
#define pb(a) push_back(a)
#define all(v) v.begin(),v.end()
#define yn(b) cout<<((b)?"Yes":"No")<<endl
#define YN(b) cout<<((b)?"YES":"NO")<<endl
#define call(a) for(auto t:a)cout<<t<<" ";cout<<endl
#define ENDL printf("\n");
#define debg(a) cout<<#a<<":"<<a<<endl;
#define SORT(a) sort(all(a));
#define INF 1LL<<60
#define inf INF
#define out(i) cout<<i<<endl;
#define allSum(a) accumulate(a.begin(),a.end(),0)
int min(int a,int b){if(a>b)return b;return a;}
int max(int a,int b){if(a>b)return a;return b;}

signed main(){
  int n;
  str s;
  cin>>n>>s;
  map<char,int> m;
  rep(i,n)m[s[i]]++;
  int res=1;
  for(char i='a';i<='z';++i){
    res*=(m[i]+1);
  }
  res--;
  out(res);
  
  return 0;
}