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)

var lines = []; var result = 0; var ans = 0;
var readline = require('readline');

var rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
});

rl.on('line', function (x) {
    lines.push(x);
})

rl.on('close', function () {
    var N = Number(lines[0]);
    var S = lines[1].split("");

    for (var i = 0; i < N; i++) {
        var alphabet_before = Array(26).fill(0)
        var alphabet_after = Array(26).fill(0)

        for (var j = 0; j < i; j++) { alphabet_before[S[j].charCodeAt(0) - 97]++ }
        for (var j = i; j < N; j++) { alphabet_after[S[j].charCodeAt(0) - 97]++ }

        for (var j = 0; j < 26; j++) {
            if (0 < alphabet_before[j] && 0 < alphabet_after[j]) { result++; }
        }
        ans = Math.max(ans, result);
        result = 0;
    }
    console.log(ans);
});