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)

function Main(input) {
  	input = input.split("\n");
  	var n = parseInt(input[0], 10);
  	s = input[1];
  	var l=new Array(26);
  	var r=new Array(26);
  	for (var i=0; i<26; i++){
      
      for (l[i]=0; l[i]<n; l[i]++){
          if (s.charCodeAt(l[i])==i+97){
           break; 
          }
      }
      
      for (r[i]=n; r[i]>=l[i]; r[i]+=-1){
          if (s.charCodeAt(r[i])==i+97){
           break; 
          }
       }    
    }
  var counter;
  var max=0;
  for (var j=0;j<n;j++){
    counter=0;
    for (var k=0; k<26; k++){
      if (j>=l[k] && j<r[k]){
       counter++; 
      }
    }
    if (counter>max){
     max=counter; 
    }
  }
  console.log('%d',max);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));