错误信息是A=3,B=2.

#include<bits/stdc++.h>
#define int long long
using namespace std;
int t,n,k,a,b,sum1,sum2,x;
bool f=0;
signed main(){
	cin>>t;
	for(int i=1;i<=t;i++){
		cin>>n>>k>>a>>b;f=0;
		if(k>n){
			cout<<0<<endl;
			for(int j=1;j<=n;j++){
				if(j%2)cout<<'a';
				else cout<<'b';
			}
			cout<<endl;
		}
		else{
			if(min(b*(n-k+1),(int)(a*(ceil(n*1.0/(k-1))-1)))==b*(n-k+1)){
				cout<< b*(n-k+1)<<endl;
				for(int j=1;j<=n;j++)cout<<(j%2)?'a':'b';
				cout<<endl;
			}
			else{
				cout << (int)(a*(ceil(n*1.0/(k-1))-1))<<endl;x=1;
				for(int j=1;j<=n;j++){
					if(x>=k-1){
						if(k==2)cout<<'z';
						else{
							if(f){
							f=0;
							if(j!=n)cout<<"yy";
							else cout<<'y';
						}
						else{
							f=1; 
							if(j!=n)cout<<"zz";
							else cout<<'z';
						}
						j++;
						x=1;
						}
					}
					else{
						f=0;
						if(j%2)cout<<'a';
						else cout<<'b';
					}
					x++;
				}
				cout<<endl;
			}
		}
	}
	return 0;
}