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>
#define REP(i, n) for(ll i = 0; i < (ll)n; i++)
#define FOR(i, a, b) for(ll i = (a); i < (ll)b; i++)
#define ALL(obj) (obj).begin(), (obj).end()
#define INF (1ll << 60)
#define sz(x) int(x.size())
using namespace std;
typedef long long ll;
using vl = vector<ll>;
using vvl = vector<vl>;
typedef double db;
typedef string str;
typedef pair<ll, ll> p;
constexpr int MOD = 1000000007;
using ll = long long;
template <class T> inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T> inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}

void print(const std::vector<int> &v) {
    std::for_each(v.begin(), v.end(), [](int x) { std::cout << x << " "; });
    std::cout << std::endl;
}
// https://ja.stackoverflow.com/questions/53484/%E3%82%A2%E3%83%83%E3%83%88%E3%82%B3%E3%83%BC%E3%83%80%E3%83%BC%E3%81%AE%E5%95%8F%E9%A1%8C%E3%81%AB%E3%81%A4%E3%81%84%E3%81%A6-colorful-subsequence
int main() {
    int N;
    string S;
    cin >> S;
    map<char, int> cnt;
    REP(i, N) { cnt[S[i]]++; }
    int ans = 1;
    for(auto hoge : cnt) {
        ans *= hoge.second;
    }
    cout << ans - 1 << endl;
    return 0;
}