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: Accepted)

/// 一开始题意就理解错了
#include <bits/stdc++.h>
using namespace std;
const int maxn = 100000 + 10,MOD = 1e9 + 7;
typedef long long LL;
int cnt[26];
char str[maxn];
LL mut(LL a,LL b){
	return (a%MOD)*(b%MOD) %MOD;
}
int main(){
	int N;
	scanf("%d%s",&N,str);
	for(int i = 0 ; i < N; ++i) ++cnt[str[i] - 'a'];
	LL ans = 1;
	for(int i = 0 ; i < 26 ; ++i){
		ans = mut(cnt[i]+1,ans);
	}
	cout<<ans-1<<endl;
	return 0;
}