学步园

贪心

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
typedef __int64 ll;
ll n,k;
int const MAXN = 100010;
char s[MAXN];
struct T{
    int x;
    ll num;
}has[50];
int cmp(T a,T b){
    if(a.num == b.num) return a.x < b.x;
    return a.num < b.num;
}
void Out(){
    for(int i = 49;i >= 0;i--){
        printf("%d %c\n",has[i].num,has[i].x + 'A');
        if(has[i].num == 0) break;
    }
}
int main(){
    cin>>n>>k;
    scanf("%s",s);
    memset(has,0,sizeof(has));
    for(int i = 0;s[i];i++){
        int x = s[i] - 'A';
        has[x].x = x;
        has[x].num++;
    }
    sort(has,has+50,cmp);
    ll ss = 0;
    for(int i = 49;i >= 0;i--){
        if(!has[i].num) break;
        if(k <= has[i].num){
            ss += k * k;
            k = 0;
        }
        else{
            ss += has[i].num * has[i].num;
            k -= has[i].num;
        }
        if(k <= 0)break;
    }
    cout<<ss<<endl;
    return 0;
}