I need to assign values to an IntArray with 1000 elements randomly. But the elements cannot be repeated. I used this code...
public int[] Numbers()
{
Random random = new Random();
int check;
for (int i = 0; i < numbers.Length; i++)
{
check = random.Next(0, 9999);
while (!numbers.Contains(check))
{
numbers[i] = check;
}
}
return numbers;
}
But then, an amount of numbers get the default values (0). What am I doing wrong ?
Your logic is slightly off - if the Contains() fails, you need to still assign that index:
for (int i = 0; i < numbers.Length; i++)
{
check = random.Next(0, 9999);
while (numbers.Contains(check))
{
// The number existed, so recompute...
check = random.Next(0, 9999);
}
numbers[i] = check;
}
You're skipping over entries if they already exist, which is why they are 0. Change your while loop:
for (int i = 0; i < numbers.Length; i++)
{
check = random.Next(0, 9999)
while (numbers.Contains(check))
{
check = random.Next(0, 9999)
}
numbers[i] = check;
}
Although a more performant (trades memory versus loops over numbers) means of generating N distinct random numbers:
int ii = 0;
var numbers = new int[N];
var used = new HashSet<int>(); // much faster on lookups than Array.Contains
while (used.Count < N)
{
var check = random.Next();
if (used.Add(check)) numbers[ii++] = check;
// alternatively: if (used.Add(numbers[ii] = check)) ii++;
}
return numbers;
You could do something like this, although it is not necessarily the most performant:
var rnd = new Random();
var result = Enumerable.Range(0, 10000).OrderBy(i => rnd.Next()).Take(1000).ToArray();
When the check fails you skip a number. Change the loop so that if the check fails you generate a new number before the loop continues
Another way to look at this will be to shuffle an order array of 1000 items You can use something like this:
public T[] Shuffle<T>(T[] array)
{
var random = _random;
for (int i = array.Length; i > 1; i--)
{
// Pick random element to swap.
int j = random.Next(i); // 0 <= j <= i-1
// Swap.
T tmp = array[j];
array[j] = array[i - 1];
array[i - 1] = tmp;
}
return array;
}
and then use it like that
int[] values = new int[1000]
for (int i=0; i<999; i++)
values[i] = i;
values = Shuffle<int>(values);
foreach (int item in values)
{
Response.Write(item);
}
Response.Write("</br>");
values = Shuffle<int>(values);
foreach (int item in values)
{
Response.Write(item); //this will generate a unique random from 0-999
}
code example taken from here
