Idea

Code

#include<iostream>
#include<cmath>
#include<algorithm>
#include<queue>
#include<string>
#include<unordered_set> 
#include<unordered_map> 
using namespace std;
typedef long long ll;
#define MAX_SIZE 10005
#define MOD 1000000009

int main(){
	int k;
	string str;
	cin>>k>>str;
	int n = str.size();
	if(n % k != 0) {
		cout<<"-1";
		return 0;
	}
	int cnt = 0;
	for(int i = 0;i< (n / k) ;i++){
		int j = 0;
		unordered_map<char,int> st;
		while(j < k){
			st[str[j * n / k + i]]++;
			j++;
		}
		int m = -1;
		for(auto item : st) m = max(m,item.second);
		cnt += k - m;
	}
	cout<<cnt;
	return 0;
}

另附：OJ评测地址