繁华模拟赛 vicent的字符串

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = ;
int n,k,a[maxn];
char cmd;
int main(){
    freopen("str.in","r",stdin);
    freopen("str.out","w",stdout);
    ios::sync_with_stdio(false);
    cin>>n>>k;
    if(k ==  && n == ){
        cout<<"a";
        return ;
    }
    if(k ==  || k > n){
        cout<<-;
        return ;
    }
    int cnt = n;
    for(int i = k;i >= ;i--){
        a[cnt] = i;
        cnt--;
    }
    for(int i = ;i <= cnt;i++){
        if(i&) a[i] = ;
        else a[i] = ;
    }
    for(int i = ;i <= n;i++){
        cmd = 'a' -  + a[i];
        cout<<cmd;
    }
    return ;
}