How to generate random numbers with out repetition in windows phone app - windows-phone-7

Question

here is the code for generating random numbers,but I am getting duplicate numbers,how can I overcome this.
void getnumbers()
{
Random r = new Random();
int[] trubyte = new int[4];
for (var x = 0; x < 4; ++x)
{
trubyte[x] = r.Next(1, 5);
}
b1.Content = trubyte[0];
b2.Content = trubyte[1];
b3.Content = trubyte[2];
b4.Content = trubyte[3];
}

Answer 1

Just get another random number if the method returns one that you already have.
void getnumbers()
{
Random r = new Random();
int num;
var trubyte = new List<int>();
for (var x = 0; x < 4; ++x)
{
do
{
num = r.Next(1, 5);
} while(trubyte.Contains(num));
trubyte[x] = num;
}
b1.Content = trubyte[0];
b2.Content = trubyte[1];
b3.Content = trubyte[2];
b4.Content = trubyte[3];
}
I'm using List instead of an array just because it offers the Contains method right away, not any other special reason.
This is not efficient if you want to generate a big list of random, unrepeated numbers (it's O(n^2) in the worst case) but for 4 numbers it's more than enough ;)

Answer 2

A random number generator function can return duplicates, because the output is random.
If you are using an RNG to generate numbers which must be unique, you will need to verify that they have not already been generated before using them.
Can't you use something like this [0] on Windows Mobile? It seems more practical than writing your own RNG.
0: http://msdn.microsoft.com/en-us/library/system.security.cryptography.randomnumbergenerator(v=vs.90).aspx

Answer 3

You have to do it by yourself, that means checking if a number was already generated.

Answer 4

You can do it like gjulianm said, but it is a long list of numbers, say 1000 you would be wasting a lot of time. So if you want a randomized list of 1000 you could proceed the following way
Initialize an array trubyte of size 1000 with trubyte[0]=1,trubyte[1]=2 and so on...
Initialize a variable arraysize=1000
run a loop 1000 times in which first extract a random number k btw 0-(arraysize-1). Your random number is a[k] which you can separately in a list. Now swap trubyte[k] with trubyte[arraysize]. And finally decrease the arraysize by one.
Another way, if you don't want the numbers while in the loop is just to use the changed list after the execution of loop
void getnumbers(){
Random r = new Random();
int num;
int[] trubyte = new int[1000];
int finalList[] = new int[1000]
for (int x = 0; x < 1000; ++x)
{
trubyte[x]=x+1;
}
int arraysize=1000;
for (var x = 0; x < 1000; ++x)
{
int k=r.Next(0, arraysize);
finalList[x]=trubyte[k];
trubyte[k]=trubyte[arraysize-1];
arraysize--;
}
//use the finalList
}

Answer 5

we can use dictionary instead of hash-set in windows phone application.
below is the code for generating distinct random numbers.
static int[] GetRandomNumbersNonrepeat(int noOfRandomNumbers, int maxValue)
{
Dictionary<int, int> randomnumbers = new Dictionary<int, int>();
while (randomnumbers.Count < maxValue)
{
Random r = new Random();
int rnum = r.Next(1, maxValue+1);
if (!randomnumbers.ContainsValue(rnum))
{
randomnumbers.Add(randomnumbers.Count + 1, rnum);
}
}
int[] rnums = randomnumbers.Values.ToArray<int>();
return rnums;
}