#include<bits/stdc++.h>
using namespace std;
#define ll long long
const ll N=2e5+10;
ll T,n,a[N];
char c,tt;
vector<char> p[N];
int main(){
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    cin>>T;
    while(T--){
		cin>>n;
		for(int i=1;i<=n;i++) cin>>a[i],p[i].clear();
		c='a';
		for(int i=1;i<=n;i++){
			if(!a[i]) cout<<(char)(c++),tt=c-1;
			else{
				ll t=p[a[i]-1].size();
				cout<<p[a[i]-1][t-1];
				tt=p[a[i]-1][t-1];
				p[a[i]-1].pop_back();
			}
			p[a[i]].push_back(tt);
		}
		cout<<"\n";
    }
	return 0;
}