题解 | #abb#

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int n= scanner.nextInt();
        if (n<3){
            System.out.println(0);
            return;
        }
        String str= scanner.next();
        long sum=0;
        char[] arr=str.toCharArray();
        int [] english=new int[26];
        for (int i = 0; i < arr.length ; i++) {
            english[arr[i]-'a']++;
        }
        for (int i = 0; i <n-2 ; i++) {
            english[arr[i]-'a']--;
            for (int j = 0; j <26 ; j++) {
                if (str.charAt(i) - 'a' != j) {
                    sum+= (english[j] * (english[j] - 1) / 2);
                }

            }
        }
        System.out.println(sum);

    }
}