B. Different is Good
题目连接：
http://www.codeforces.com/contest/672/problem/B
Description
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.
Input
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.
Output
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.
Sample Input
2
aa
Sample Output
1
题意
给你一个字符串，你可以把这个字符串的字符改成其他的字符，然后让你使得里面的所有子串都不一样
问你最少改多少个
题解：
子串都不一样的话，其实就是所有的字符都不一样，记录一下这个就好了
代码
#include<bits/stdc++.h>
using namespace std;
string s;
int m[26];
int main()
{
cin>>s;
cin>>s;
for(int i=0;i<s.size();i++)
m[s[i]-'a']++;
int add1=0,add2=0;
for(int i=0;i<26;i++)
{
if(m[i]==0)add2++;
else add1+=(m[i]-1);
}
if(add2<add1)cout<<"-1"<<endl;
else cout<<add1<<endl;
}