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;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<double,int> pdi;
bool cnta[30], cntb[30];
int main()
{
    int n;
    scanf("%d", &n);
    string s;
    cin >> s;
    int cnt = 0, ans = 0;
    for(int i = 1; i < n; i++)
    {
        cnt = 0;
        memset(cnta,0,sizeof(cnta));
        memset(cntb,0,sizeof(cntb));
        for(int j = 0; j < i; j++)
        {
            cnta[s[j]-'a']=1;
        }
        for(int j = i; j < n; j++)
        {
            cntb[s[j]-'a']=1;
        }
        for(int i = 0; i < 26; i++)
        {
            if(cnta[i]&&cntb[i])
                cnt++;
        }
        ans = max(ans, cnt);
    }
    printf("%d\n", ans);
}