def compress(A):
    S = sorted(A)
    D = dict()
    for i in range(len(S)):
        D[S[i]] = i
    return D

def func(P):
    R = []
    IDX = set()
    for x in X:
        l, r = x-P, x+P
        if l < 0:
            R.append((l%L, 1))
            IDX.add(l%L)
            l = 0
        if L < r:
            R.append((0, 1))
            IDX.add(0)
            R.append((r%L+0.5, -1))
            IDX.add(r%L+0.5)
            r = L
        R.append((l, 1))
        IDX.add(l)
        if r < L:
            R.append((r+0.5, -1))
            IDX.add(r+0.5)
    IDX = compress(IDX)
    C = [0]*len(IDX)
    for n, d in R:
        C[IDX[n]] += d
    for i in range(1, len(IDX)):
        C[i] += C[i-1]
    return K <= min(C)

for _ in range(int(input())):
    N, L, K = map(int, input().split())
    X = list(map(int, input().split()))

    left = 0
    right = (L+1)//2
    while left+1 < right:
        mid = (left+right)//2
        if not func(mid):
            left = mid
        else:
            right = mid
    
    print(right)