#include<stdio.h>
#include<string.h>
#define N 100
#define INF 2000000000
int b[N];
char s[100001];
struct nodee{
int parent,lson,rson,visit,weight;
}a[N];
int main() {
int t,n,m,count,i,j,max1,max2,total,sum;
scanf("%d",&t);
while(t--) {
scanf("%d",&total);
scanf("%s",s);
count=0;
memset(b,0,sizeof(b));
for(i=0;s[i];i++)
b[s[i]-'a']++;
j=1;
for(i=0;i<26;i++)
if(b[i]) {
a[j].lson=a[j].rson=a[j].parent=a[j].visit=0;
a[j].weight=b[i];
j++;
}
count=j-1;
for(i=1;i<count;i++) {//creat 哈夫曼树
max1=max2=INF;
n=m=0;
for(j=1;j<count+i;j++) {
if(!a[j].visit&&a[j].weight<max1) {
m=n;
max2=max1;
n=j;
max1=a[j].weight;
}
else
if(!a[j].visit&&a[j].weight<max2) {
m=j;
max2=a[j].weight;
}
}
a[count+i].weight=a[n].weight+a[m].weight;
a[count+i].lson=n;
a[count+i].rson=m;
a[count+i].visit=0;//这个要初始化，不然不对
a[n].parent=count+i;
a[m].parent =count+i;
a[n].visit=1;
a[m].visit=1;
}
sum=0;
for(i=count+1;i<=count*2-1;i++)//相当于求所有叶节点的带权路径长度
sum+=a[i].weight;
if(count==1)
sum=a[1].weight;
if(sum<=total)
printf("yes
");
else
printf("no
");
}
return 0;
}