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 JavaScript (node.js v5.12) (judge verdict: Accepted)

'use strict'

const inArray = (needle, haystack) => haystack.some(item => item === needle)

const main = (input) => {
    const strings = input.split('\n')[1].split('')

    let ans = 0
    for(let i = 1; i < strings.length; i++){
        let first = strings.slice(0, i)
        let last = strings.slice(i)
        let f2 = [...new Set(first)]
        let tmp = 0
        for(let j = 0; j < f2.length; j++){
            if(inArray(f2[j], last)){
                tmp++
            }
        }
        if(ans < tmp){
            ans = tmp
        }
    }
    console.log(ans)
}

main(require('fs').readFileSync('/dev/stdin', 'utf-8'))