Colorful Subsequence

最新推荐文章于 2019-09-14 10:59:44 发布

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最新推荐文章于 2019-09-14 10:59:44 发布

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分类专栏：算法和数据结构

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本文介绍了一种算法，用于计算给定字符串中所有字符不同的子序列数量，并提供了一个具体的C++实现示例。

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题目描述

You are given a string S of length N. Among its subsequences, count the ones such that all characters are different, modulo 109+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≤N≤100000
·S consists of lowercase English letters.
·|S|=N

输入

Input is given from Standard Input in the following format:

N
S

输出

Print the number of the subsequences such that all characters are different, modulo 109+7.

样例输入

abcd

样例输出

#include<cstdio>
#include<cstring>
#include<map>
using namespace std;
map<char,int>mp;
const int maxn = 100000+10;
const long long mod = 1e9+7;
char a[maxn];
int main()
{
    int n;
    scanf("%d%s",&n,&a);
    for(int i=0;i<n;i++)
    {
        mp[a[i]]++;
    }
    long long ans=1;
    for(char i='a';i<='z';i++)
    {
        ans*=(mp[i]+1);
        ans%=mod;
    }
    printf("%lld\n",ans-1);
}