Q=int(input())
for _ in range(Q):
    N,L,K=map(int,input().split())
    A=list(map(int,input().split()))
    LL=L
    h=[]
    A.sort()
    for i in range(N):
        h.append(2*A[i])
    for i in range(N):
        h.append(2*L+2*A[i])
    for i in range(N):
        h.append(4*L+2*A[i])
    from bisect import bisect_left,bisect_right
    l=0
    r=2*L
    while True:
        if l==r:
            break
        m=(l+r)//2
        p=[]
        ans=True
        for i in range(N):
            x=2*A[i]+m+1
            x%=2*LL
            p.append(x)
            y=2*A[i]-(m+1)
            y%=2*LL
            p.append(y)
        for x in p:
            y=x+2*LL
            count2=bisect_right(h,y+m)
            count1=bisect_right(h,y-(m+1))
            c=count2-count1
            if c<K:
                ans=False
        if ans==True:
            r=m
        else:
            l=m+1
    print((l+1)//2)