#include<bits/stdc++.h>
using namespace std;
struct H{long double w;long long x,y;}a[1000007];
bool cmp(H x,H y){return x.w<y.w;}
long long n,m,k,l,s,wl,fl,ts;
long double f;
const long double eps=1e-9,weps=1e-12;
string st;
bool ch(long double d){
	long double ma=-1e9,mi=1e9;wl=1e9;++ts;
	for(int i=0;i<=n;i++){
		ma=max(ma,a[i].y+a[i].x*-(f+d));
		if(fabs(ma-(a[i].y+a[i].x*-(f+d)))>weps)wl=min(wl,a[i].x+1);
	}
	for(int i=n;i>=0;i--){
		mi=min(mi,a[i].y+a[i].x*-(f+d));
		if(fabs(mi-(a[i].y+a[i].x*-(f+d)))>weps)wl=min(wl,a[i].x+1);
	}
	ma=-1e9;mi=1e9;
	for(int i=0;i<=n;i++){
		ma=max(ma,a[i].y+a[i].x*-(f-d));
		if(fabs(ma-(a[i].y+a[i].x*-(f-d)))>weps)wl=min(wl,a[i].x+1);
	}
	for(int i=n;i>=0;i--){
		mi=min(mi,a[i].y+a[i].x*-(f-d));
		if(fabs(mi-(a[i].y+a[i].x*-(f-d)))>weps)wl=min(wl,a[i].x+1);
	}
	return (wl!=1e9);
}
int main(){
//	freopen("c.in","r",stdin);
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	int T,sd;
	cin>>T;
	while(T--){
		cin>>sd;fl=1;
		cin>>f>>st;n=st.size();a[0].w=a[0].x=a[0].y=0;
		for(int i=1;i<=n;i++)a[i].w=-f+(st[i-1]-'0')+a[i-1].w,a[i].x=i,a[i].y=a[i-1].y+st[i-1]-'0';
		sort(a,a+n+1,cmp);
		long double l=0,r=1;
		while((r-l)>eps){
			long double mid=(l+r)/2;
			if(ch(mid))r=mid,fl=wl;
			else l=mid;
		}
		cout<<fl-1<<'\n';
	}
	
}