#include<stdio.h>
long long int h[40004], hl;
long long int comp_h(long long int a, long long int b)
{
	if (h[a] > h[b])
		return 1;
	else
		return -1;
}
void swap_h(long long int a, long long int b)
{
	long long int f = h[a];
	h[a] = h[b];
	h[b] = f;
	return;
}
void push(long long int ne)
{
	h[hl] = ne;
	long long int p = hl++;
	for (; p > 0; p = (p - 1) / 2)
		if (comp_h((p - 1) / 2, p) > 0)
			swap_h((p - 1) / 2, p);
	return;
}
long long int pop()
{
	swap_h(0, --hl);
	long long int p = 0;
	for (;;)
	{
		if (2 * p + 2 < hl)
		{
			if (comp_h(2 * p + 1, 2 * p + 2) > 0)
			{
				if (comp_h(p, 2 * p + 2) > 0)
					swap_h(p, 2 * p + 2);
				p = 2 * p + 2;
			}
			else
			{
				if (comp_h(p, 2 * p + 1) > 0)
					swap_h(p, 2 * p + 1);
				p = 2 * p + 1;
			}
		}
		else if (2 * p + 1 < hl)
		{
			if (comp_h(p, 2 * p + 1) > 0)
				swap_h(p, 2 * p + 1);
			p = 2 * p + 1;
		}
		else
			break;
	}
	return h[hl];
}
long long int x[20004];
long long int xx[40004], s, cnt[400005];
long long int find(long long int y)
{
	long long int min, mid, max;
	min = -1;
	max = s;
	while (max - min > 1)
	{
		mid = (max + min) / 2;
		if (xx[mid] < y)
			min = mid;
		else
			max = mid;
	}
	return max;
}
void solve()
{
	long long int n, l, k;
	scanf("%lld %lld %lld", &n, &l, &k);
	long long int i;
	for (i = 0; i < n; i++)
		scanf("%lld", &x[i]);
	long long int min, mid, max;
	min = 0;
	max = (l + 1) / 2;
	long long int f;
	while (max - min > 1)
	{
		mid = (max + min) / 2;
		hl = 0;
		for (i = 0; i < n; i++)
		{
			push((x[i] - min + l) % l);
			push((x[i] + mid) % l);
		}
		xx[0] = 0;
		s = 1;
		while (hl > 0)
		{
			xx[s] = pop();
			if (xx[s - 1] != xx[s])
				s++;
		}
		for (i = 0; i < s; i++)
			cnt[i] = 0;
		for (i = 0; i < n; i++)
		{
			if (x[i] - mid < 0)
			{
				cnt[find(x[i] - mid + l)]++;
				cnt[0]++;
			}
			else
				cnt[find(x[i] - mid)]++;
			if (x[i] + mid < l)
				cnt[find(x[i] + mid)]--;
			else
			{
				cnt[0]++;
				cnt[find(x[i] + mid - l)]--;
			}
		}
		for (i = 1; i < s; i++)
			cnt[i] += cnt[i - 1];
		f = 0;
		for (i = 0; i < s; i++)
			if (cnt[i] < k)
				f++;
		if (f > 0)
			min = mid;
		else
			max = mid;
	}
	printf("%lld\n", max);
	return;
}
int main()
{
	int t;
	scanf("%d", &t);
	for (; t > 0; t--)
		solve();
	return 0;
}