for _ in range(int(input())):
    n, l, k = map(int, input().split())
    x = sorted(map(int, input().split()))
    lb = 0
    ub = (l + 1) // 2
    while ub - lb > 1:
        c = (lb + ub) // 2
        evs = []
        now = 0
        for xi in x:
            if 0 <= xi - c:
                evs.append((xi - c, -1))
            else:
                evs.append((xi - c + l, -1))
                now += 1
            if xi + c < l:
                evs.append((xi + c, 1))
            else:
                evs.append((xi + c - l, 1))
                now += 1
        evs.sort()
        ok = now >= k
        if c == 171:
            print(x, now)
            print(*evs, sep='\n')
        for t, sub in evs:
            now -= sub
            if now < k:
                ok = False
        if ok:
            ub = c
        else:
            lb = c
    print(ub)