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 (1.15.1) (judge verdict: Accepted)

use std::io;
use std::collections::HashSet;
use std::cmp::max;

fn main() {
	let mut buf = String::new();
	io::stdin().read_line(&mut buf).expect("");
	let mut buf = String::new();
	io::stdin().read_line(&mut buf).expect("");
	let s = buf.trim();
	let mut ret = 0;
	for i in 1..s.len() {
		let mut set1:HashSet<char> = HashSet::new();
		let mut set2:HashSet<char> = HashSet::new();
		let s1 = &s[..i].to_string();
		let s2 = &s[i..].to_string();
		let vs1:Vec<char> = s1.chars().collect();
		let vs2:Vec<char> = s2.chars().collect();
		for i in vs1 {
			set1.insert(i);
		}
		for i in vs2 {
			set2.insert(i);
		}
		let intersection:HashSet<_> = set1.intersection(&set2).collect();
		ret = max(intersection.len(), ret);
	}
	println!("{}", ret);
}