A wise man told Kerem "Different is good" once, so Kerem wants all things in his life to be different.

Kerem recently got a string s consisting of lowercase English letters. Since Kerem likes it when things are different, he wants all substrings of his string s to be distinct. Substring is a string formed by some number of consecutive characters of the string. For example, string "aba" has substrings "" (empty substring), "a", "b", "a", "ab", "ba", "aba".

If string s has at least two equal substrings then Kerem will change characters at some positions to some other lowercase English letters. Changing characters is a very tiring job, so Kerem want to perform as few changes as possible.

Your task is to find the minimum number of changes needed to make all the substrings of the given string distinct, or determine that it is impossible.

The first line of the input contains an integer n (1?≤?n?≤?100?000) — the length of the string s.

The second line contains the string s of length n consisting of only lowercase English letters.

If it‘s impossible to change the string s such that all its substring are distinct print -1. Otherwise print the minimum required number of changes.

初看嚇了一跳還以為這麽多子串怎麽辦，不過仔細一想不就是保證每一位的字母都不一樣嗎。當n>26時字母不夠用當然-1

否則就是統計那些重復的字符數即可

#include <cstdio>
#include <cctype>
#include <stdlib.h>
#include <iostream>
#include <cmath>
#include <iomanip>
#include <cstring>
#include <algorithm>
#include <string>
#include <vector>
#include <map>

using namespace std;
typedef long long LL;
int n;
char s[100005];
int appear[26] = {0};
int main()
{
  // freopen("test.in","r",stdin);
  cin >> n;
  cin >> s;
  int len = strlen(s);
  if (len > 26){
    cout << -1; return 0;
  }
  for (int i=0;i<len;i++){
    appear[s[i] - ‘a‘] ++;
    // cout << s[i];
  }
  int total = 0 ;
  for (int i=0;i<26;i++){
    if (appear[i] > 1){
      total += appear[i] - 1;
    }
  }
  cout << total;
  return 0;
}

Codeforce 672B. Different is Good