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 Rust (1.42.0) (judge verdict: Accepted)

use proconio::input;
use proconio::marker::*;
use std::collections::HashMap;

fn main() {
  input! {
    n: usize,
    chars: String
  }
  
  let mut left = vec![0;26];
  let mut right = vec![0;26];
  for v in chars.as_bytes().iter() {
    let i = (v - 97u8) as usize;
    right[i] += 1;
  }
  
  let mut max = 0;
  for v in chars.as_bytes().iter() {
    let i = (v - 97u8) as usize;
    right[i] -= 1;
    left[i] += 1;
    
    let mut temp = 0;
    for ii in 0..26 {
      if 0 < right[ii] && 0 < left[ii] {
        temp += 1;
      }
    }
    max = std::cmp::max(max, temp);
  }
   
  println!("{}", max);
}