code:

public static void setWorldMonsters()
{
Random random = new Random(Main.worldID);
int num = random.Next(3);
int num2 = random.Next(3);
while (num == num2)
{
num = random.Next(3);
}
for (int i = 0; i < 2; i++)
{
int num3 = num;
if (i == 1)
{
num3 = num2;
}
for (int j = 0; j < 3; j++)
{
if (num3 == 0)
{
NPC.cavernMonsterType[i, j] = random.Next(494, 496);
}
else
{
if (num3 == 1)
{
NPC.cavernMonsterType[i, j] = random.Next(496, 498);
}
else
{
NPC.cavernMonsterType[i, j] = random.Next(498, 507);
}
}
}
}
}