1979D - Fixing a Binary String - CodeForces Solution

t=int(input())
for i in range(t):
    n,m=map(int,input().split())
    s=input()
    l=list(s)
    a=s.count('0')
    b=s.count('1')
                                if(n==1):
        print(n)
    elif(n==2):
        if(a==b and a==1 and m==1):
            print(1)
        elif(a!=b and m==2):
            print(1)
        else:
            print(-1)
    else:
        f1=0
        f2=0
        c=1
        d=-1
        e=0
        for i in range(len(l)-1):
            if(l[i]==l[i+1]):
                c+=1
            else:
                if(c!=m):
                    f2=1
                    if(c<m):
                        d=i+1
                    else:
                        d=i+1-(m)
                    break
                else:
                    c=1
        if(c!=m):
            f2=1
            if(c<m):
                d=i+1
            else:
                d=i+1-(m)
        if(d==-1):
            print(n)
        else:
            l=l[d:]+l[:d][::-1]
            c=1
            for i in range(len(l)-1):
                if(l[i]==l[i+1]):
                    c+=1
                else:
                    if(c!=m):
                        f1=1
                        print(-1)
                        break
                    else:
                        c=1
            if(c!=m and f1==0):
                        f1=1
                        print(-1)
            if(f1==0):
                print(d)