Problem:
Score : 200 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.
We will cut this string at one position into two strings X and Y.
Here, we would like to maximize the number of different letters contained in both X and Y.
Find the largest possible number of different letters contained in both X and Y when we cut the string at the optimal position.

Constraints

2 \leq N \leq 100

|S| = N

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the largest possible number of different letters contained in both X and Y.

Sample Input 1

6
aabbca

Sample Output 1

2

If we cut the string between the third and fourth letters into X = aab and Y = bca, the letters contained in both X and Y are a and b.
There will never be three or more different letters contained in both X and Y, so the answer is 2.

Sample Input 2

10
aaaaaaaaaa

Sample Output 2

1

However we divide S, only a will be contained in both X and Y.

Sample Input 3

45
tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir

Sample Output 3

9

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;
char str[200];
int n;
int f(int x)
{
    int ans=0;
    set<char> s1,s2;
    for(int i=0;i<=x-1;i++)
        s1.insert(str[i]);
    for(int i=x;i<n;i++)
    {
        if(!s2.count(str[i]))
         ans+=s1.count(str[i]);
         s2.insert(str[i]);
    }

    return ans;
}
int main(){

    scanf("%d%s",&n,str);
    int ans=0;
    for(int i=1;i<=n-1;i++)
      ans=max(ans,f(i));
    printf("%d\n",ans);
    return 0;
}