We Keep Coding

How can I make so that my Values dont repeat with Random.Range()? [duplicate]

Basically I'm creating a program to randomly generate 6 unique lottery numbers so there is no duplicates in the same line, here is the code I have so far...
//Generate 6 random numbers using the randomiser object
int randomNumber1 = random.Next(1, 49);
int randomNumber2 = random.Next(1, 49);
int randomNumber3 = random.Next(1, 49);
int randomNumber4 = random.Next(1, 49);
int randomNumber5 = random.Next(1, 49);
int randomNumber6 = random.Next(1, 49);
textBox1.Text = randomNumber1.ToString();
textBox2.Text = randomNumber2.ToString();
textBox3.Text = randomNumber3.ToString();
textBox4.Text = randomNumber4.ToString();
textBox5.Text = randomNumber5.ToString();
textBox6.Text = randomNumber6.ToString();
}
I'm getting random numbers but sometimes there is the same number on the same line, how do I make each number unique????
Thanks in advance

You need to store them in a collection and each time you pick a new number you need to make sure it's not present already, otherwise you need to generate a new number until you find a unique number.
Instead of this, I would generate a sequence between 1 and 49, shuffle them and pick 6 number out of the sequence, for example:
var rnd = new Random();
var randomNumbers = Enumerable.Range(1,49).OrderBy(x => rnd.Next()).Take(6).ToList();

You can't. You've only specified that each number be a random number from 1 to 49, not that it shouldn't match any duplicates.
Since you've got a relatively small set of numbers, your best bet is probably to draw the random numbers, put them into a HashSet, then if you need more, pull more. Something like this:
HashSet<int> numbers = new HashSet<int>();
while (numbers.Count < 6) {
numbers.Add(random.Next(1, 49));
}
Here you're taking advantage of the HashSet's elimination of duplicates. This won't work with a List or other collection.

Returning repeat values is a necessity in order for a generator to satisfy a necessary statistical property of randomness: the probability of drawing a number is not dependent on the previous numbers drawn.
You could shuffle the integers in the range 1 to 49 and return the first 6 elements. See http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle for more details on such a shuffler.
However, I think you get a slight statistical bias by doing this.
The best way is probably to use random.Next(1, 49); and reject any repeat. That will be free from statistical bias and the fact that you're only wanting 6 from 49 possibilities, the number of collisions will not slow the algorithm appreciably.

Using this extension method for reservoir sampling:
public static IList<T> TakeRandom<T>(
this IEnumerable<T> source, int count, Random random)
{
var list = new List<T>(count);
int n = 1;
foreach (var item in source)
{
if (list.Count < count)
{
list.Add(item);
}
else
{
int j = random.Next(n);
if (j < count)
{
list[j] = item;
}
}
n++;
}
return list;
}
You can sample your collection like this:
var random = new Random();
var numbers = Enumerable.Range(1, 49).TakeRandom(6, random);
numbers.Shuffle(random);
Note the returned numbers will be uniformly sampled out of all (49 choose 6) possibilities for a set of 6 numbers out of {1, 2, ..., 49}, but they will neither remain in order nor be uniformly shuffled. If you want to have the order randomized as well, you can easily do a standard Fisher-Yates shuffle afterwards.
public static void Shuffle<T>(this IList<T> list, Random random)
{
for (int i = 0; i < list.Count; i++)
{
int j = random.Next(i, list.Count);
T temp = list[j];
list[j] = list[i];
list[i] = temp;
}
}
Note a more heavily optimized version of Fisher-Yates shuffle can be found in this answer: Randomize a List<T>

List<int> aux = new List<int>();
while(aux.Count < 6)
{
int rnd = random.Next(1,49);
if(!aux.Contains(rnd))aux.add(rnd);
}
if you put all Texbox in the same panel you can do that
int j = 0;
foreach(Control x in MyPanel.Controls)
{
if(x is TexBox)
{
x.Text = aux[j].toString();
j++;
}
}

It's my solution: generate array of number
/// <summary>
/// auto generate a array with number element and max value is max
/// </summary>
/// <param name="number">number element of array</param>
/// <param name="max">max value of array</param>
/// <returns>array of number</returns>
public static int[] createRandomArray(int number, int max)
{
List<int> ValueNumber = new List<int>();
for (int i = 0; i < max; i++)
ValueNumber.Add(i);
int[] arr = new int[number];
int count = 0;
while (count < number)
{
Random rd = new Random();
int index = rd.Next(0,ValueNumber.Count -1);
int auto = ValueNumber[index];
arr[count] = auto;
ValueNumber.RemoveAt(index);
count += 1;
}
return arr;
}

It's too late but I use a Method named M_Randomizer created by me. It may look as too much work, but it's technique is different from traditional which is based on generating a random number and checking the previously generated list for uniqueness. This code while generating a new random number, never looks for the previously generated. And if we talk about touching all combinations, I have tested this method till 9 factorial, maybe little bias for some but it touches all.
using System;
class Randomizer
{
public int[] M_Randomizer(int x)
{
bool b = false;
if (x < -1)
{
b = true;
x = -1 * x;
}
if(x == -1)
x = 0;
if (x < 2)
return new int[x];
int[] site;
int k = new Random(Guid.NewGuid().GetHashCode()).Next() % 2;
if (x == 2)
{
site = new int[2];
site[0] = k;
site[1] = 1 - site[0];
return site;
}
else if (x == 3)
{
site = new int[3];
site[0] = new Random(Guid.NewGuid().GetHashCode()).Next(0, 3);
site[1] = (site[0] + k + 1) % 3;
site[2] = 3 - (site[0] + site[1]);
return site;
}
site = new int[x];
int a = 0, m = 0, n = 0, tmp = 0;
int[] p = M_Randomizer(3);
int[] q;
if (x % 3 == 0)
q = M_Randomizer(x / 3);
else
q = M_Randomizer((x / 3) + 1);
if (k == 0)
{
for (m = 0; m < q.Length; m++)
{
for (n = 0; n < p.Length && a < x; n++)
{
tmp = (q[m] * 3) + p[n];
if (tmp < x)
{
site[a] = tmp;
a++;
}
}
}
}
else
{
while (n < p.Length)
{
while (a < x)
{
tmp = (q[m] * 3) + p[n];
if (tmp < x)
{
site[a] = tmp;
a++;
}
m = m + k;
if (m >= q.Length)
break;
}
m = m % q.Length;
n++;
}
}
a = (new Random(Guid.NewGuid().GetHashCode()).Next() % 2) + 1;
k = new Random(Guid.NewGuid().GetHashCode()).Next() % 10;
if (k > 5)
for (int i = a; i < k; i++)
while (a < site.Length)
{
if (k % (a + 1) == 0)
{
tmp = site[a - 1];
site[a - 1] = site[a];
site[a] = tmp;
}
a = a + 2;
}
k = new Random(Guid.NewGuid().GetHashCode()).Next() % 10;
if (k > 5)
{
n = x / 2;
k = 0;
if (x % 2 != 0)
k = (new Random(Guid.NewGuid().GetHashCode()).Next() % 2);
p = new int[n + k];
m = (x - n) - k;
for (a = 0; m < x; a++, m++)
p[a] = site[m];
m = n + k;
for (a = (x - m) - 1; a >= 0; a--, m++)
site[m] = site[a];
for (a = 0; a < p.Length; a++)
site[a] = p[a];
}
int[] site2;
int[] site3 = new int[x];
if (b)
return site;
else
site2 = M_Randomizer(-1 * x);
for (a = 0; a < site.Length; a++)
site3[site2[a]] = site[a];
return site3;
}
public int[] M_Randomizer(int x, int start)
{
int[] dm = M_Randomizer(x);
for(int a = 0; a < x; a++)
dm[a] = dm[a] + start;
return dm;
}
}

Look at using an array to hold your 6 numbers.
Each time you generate one, loop through the array to make sure it is not already there. If it is, then generate another & loop again until you have a non-match.

It's so easy with array and OOP (Object Oriented Programming). Before you start you have to add Linq (using System.Linq) library to your project.
Random random = new Random();
int[] array = new int[6];
int number;
for (int i = 0; i < 6; i++)
{
number = random.Next(1, 50);
if (!array.Contains(number)) //If it's not contains, add number to array;
array[i] = number;
else //If it contains, restart random process
i--;
}
for (int i = 1; i < 7; i++)
{
foreach (Control c in this.Controls) //Add random numbers to all Textboxes
{
if (c is TextBox && c.Name.EndsWith(i.ToString()))
{
c.Text = array[i - 1].ToString();
}
}
}

A functional approach could be to generate an infinite sequence of random numbers, filter out non-unique numbers and take the number of unique numbers you need.
For example:
private IEnumerable<int> RandomDigitStream(int seed)
{
Random random = new Random(seed);
while (true)
{
yield return random.Next(DIGIT_MIN, DIGIT_MAX);
}
}
private List<int> GenerateUniqueRandomNumbers(int seed, int count)
{
// Assert that DIGIT_MAX - DIGIT_MIN > count to ensure
// algorithm can finish
return RandomDigitStream(seed)
.Distinct()
.Take(count)
.ToList();
}
The efficiency of this algorithm is mainly dependent on how Distinct is implemented by the .NET team. Its memory usage would grow with the number of digits you require and the range of digits produced by the random function. It also has an unpredictable running time as it depends on the probability distribution of the random function. In fact it is possible for this algorithm to get stuck in an infinite loop if the range of digits produced by the random algorithm is less than the number of digits you require.
Looking at it practically however, it should be fine for a small amount of digits but if you are looking at a large number (100 +) you might want to look at other methods.
It would be more efficient to craft a random algorithm that only produces unique numbers in the first place if that is even possible without using a lookup table.

Here is a small program using recursion to generate number lines, and also uses recursion to randomize and get unique numbers.
using System;
using System.Linq;
using System.Collections.Generic;
public class Program
{
public static Random random;
public static List<int> lottoNumbers = Enumerable.Range(1, 49).ToList();
public static void Main()
{
random = new Random((int)DateTime.Now.Ticks);
var LinesToGenerate = 10;
GenerateNumbers(LinesToGenerate);
}
public static void GenerateNumbers(int LineCount)
{
int[] SelectedNumbers = new int[6];
for (var i = 0; i < 6; i++)
{
var number = GetRandomNumber(lottoNumbers.ToArray());
while (SelectedNumbers.Contains(number))
number = GetRandomNumber(lottoNumbers.ToArray());
SelectedNumbers[i] = number;
}
var numbersOrdered = SelectedNumbers.OrderBy(n => n).Select(n => n.ToString().PadLeft(2, '0'));
Console.WriteLine(string.Join(" ", numbersOrdered));
if (LineCount > 1)
GenerateNumbers(--LineCount);
}
//Recursively and randomly removes numbers from the array until only one is left, and returns it
public static int GetRandomNumber(int[] arr)
{
if (arr.Length > 1)
{
//Remove random number from array
var r = random.Next(0, arr.Length);
var list = arr.ToList();
list.RemoveAt(r);
return GetRandomNumber(list.ToArray());
}
return arr[0];
}
}

Yes. Use array.
Loop how many times you want:
Generate a random number,
Loop through array and compare all with the generated number.
If there's a match then loop again till there's no match.
Then store it.
Done:)

MaxCounters codility understanding

I have wanted to try some challenges on Codility and started from beginning. All assignments were relatively easy up to the one called MaxCounters. I do not believe that this one is especially hard although it is the first one marked as not painless.
I have read the task and started coding in C# language:
public static int[] maxPart(int N, int[] A){
int[] counters = new int[N];
for(int i = 0; i < A.Length; i++){
for(int j = 0; j < counters.Length; j++){
if(A[i] == counters[j] && (counters[j] >= 1 && counters[j] <= N )){
counters [j] = counters [j] + 1;
}
if(A[i] == N + 1 ){
int tmpMax = counters.Max ();
for(int h = 0; h < counters.Length; h++){
counters [h] = tmpMax;
}
}
}
}
return counters;
}
Having 3 loops of course makes it really slow, but lets leave it for later. My concern is how I understood this like this and all the other people see it like on this question here.
From the assignment's description.
it has 2 actions:
increase(X) − counter X is increased by 1,
max counter − all counters are set to the maximum value of any
counter.
which occur under conditions:
if A[K] = X, such that 1 ≤ X ≤ N, then operation K is increase(X),
if A[K] = N + 1 then operation K is max counter.
Both conditions are stated in the code above. Obviusly it is wrong but I am confused, and I do not know how could I understand it differently.
Why is this code wrong, what am I missing from task description?
One of the top rated answers looks like this:
public int[] solution(int N, int[] A) {
int[] result = new int[N];
int maximum = 0;
int resetLimit = 0;
for (int K = 0; K < A.Length; K++)
{
if (A[K] < 1 || A[K] > N + 1)
throw new InvalidOperationException();
if (A[K] >= 1 && A[K] <= N)
{
if (result[A[K] - 1] < resetLimit) {
result[A[K] - 1] = resetLimit + 1;
} else {
result[A[K] - 1]++;
}
if (result[A[K] - 1] > maximum)
{
maximum = result[A[K] - 1];
}
}
else
{
// inefficiency here
//for (int i = 0; i < result.Length; i++)
// result[i] = maximum;
resetLimit = maximum;
}
}
for (int i = 0; i < result.Length; i++)
result[i] = Math.max(resetLimit, result[i]);
return result;
}
This code results with 100% on Codility.
Question:
I would like to know how the author knew from the task to use result[A[K] - 1]? What would resetLimit represent?
Maybe I completely misunderstood the question due to my English I am not sure. I just can not go over it.
EDIT:
Based on my code provided, how did I misunderstood the assignment? Generally I am asking for explanation of the problem. Whether to explain what needs to be done, or take the code as correct result and provide and explanation why is this done this way?

In my opinion you somehow mixed the index of the counter (values in A) and the value of the counter (values in counter). So there is no magic in using A[i]-1 - it is the value X from the problem description (adjusted to 0-based index).
My naive approach would be, the way I understood the problem (I hope it makes clear, what your code is doing wrong):
public static int[] maxPart(int N, int[] A){
int[] counters = new int[N];
for(int i = 0; i < A.Length; i++){
int X=A[i];
if(X>=1 && X<=N){ // this encodes increment(X), with X=A[i]
counters [X-1] = counters [X-1] + 1; //-1, because our index is 0-based
}
if(X == N + 1 ){// this encodes setting all counters to the max value
int tmpMax = counters.Max ();
for(int h = 0; h < counters.Length; h++){
counters [h] = tmpMax;
}
}
}
}
return counters;
}
Clearly, this would be too slow as the complexity isO(n^2) with n=10^5 number of operations (length of the array A), in the case of the following operation sequence:
max counter, max counter, max counter, ....
The top rated solution solves the problem in a lazy manner and does not update all values explicitly every time a max counter operation is encountered, but just remembers which minimal value all counters must have after this operation in resetLimit. Thus, every time he must increment a counter, he looks up whether its value must be updated due to former max counter operations and makes up for all max counter operation he didn't execute on this counter
if(result[A[K] - 1] < resetLimit) {
result[A[K] - 1] = resetLimit + 1;
}
His solution runs in O(n) and is fast enough.

Here is my solution in JavaScript.
const maxCounters = (N, A) => {
for (let t = 0; t < A.length; t++) {
if (A[t] < 1 || A[t] > N + 1) {
throw new Error('Invalid input array A');
}
}
let lastMaxCounter = 0; // save the last max counter is applied to all counters
let counters = []; // counters result
// init values by 0
for (let i = 0; i < N; i++) {
counters[i] = 0;
}
let currentMaxCounter = 0; // save the current max counter each time any counter is increased
let maxApplied = false;
for (let j = 0; j < A.length; j++) {
const val = A[j];
if (1 <= val && val <= N) {
if (maxApplied && counters[val - 1] < lastMaxCounter) {
counters[val - 1] = lastMaxCounter;
}
counters[val - 1] = counters[val - 1] + 1;
if (currentMaxCounter < counters[val - 1]) {
currentMaxCounter = counters[val - 1];
}
} else if (val === N + 1) {
maxApplied = true;
lastMaxCounter = currentMaxCounter;
}
}
// apply the lastMaxCounter to all counters
for (let k = 0; k < counters.length; k++) {
counters[k] = counters[k] < lastMaxCounter ? lastMaxCounter : counters[k];
}
return counters;
};

Here is C# solution give me 100% score
public int[] solution(int N, int[] A) {
int[] operation = new int[N];
int max = 0, globalMax = 0;
foreach (var item in A)
{
if (item > N)
{
globalMax = max;
}
else
{
if (operation[item - 1] < globalMax)
{
operation[item - 1] = globalMax;
}
operation[item - 1]++;
if (max < operation[item - 1])
{
max = operation[item - 1];
}
}
}
for (int i = 0; i < operation.Length; i++)
{
if (operation[i] < globalMax)
{
operation[i] = globalMax;
}
}
return operation;
}

Here is a pretty elegant soulution in Swift:
public func solution(_ N : Int, _ A : inout [Int]) -> [Int] {
var globalMax = 0
var currentMax = 0
var maximums: [Int: Int] = [:]
for x in A {
if x > N {
globalMax = currentMax
continue
}
let newValue = max(maximums[x] ?? globalMax, globalMax) + 1
currentMax = max(newValue, currentMax)
maximums[x] = newValue
}
var result: [Int] = []
for i in 1...N {
result.append(max(maximums[i] ?? globalMax, globalMax))
}
return result
}

Try this Java snippet. Its more readable and neater, you don't need to worry about bounds check and might evacuate your first findings related to the more efficient approach you have found, btw the max is on the main forloop not causing any overhead.
public final int[] solution(int N, int[] A)
{
int condition = N + 1;
int currentMax = 0;
int lastUpdate = 0;
int[] counters = new int[N];
for (int i = 0; i < A.length; i++)
{
int currentValue = A[i];
if (currentValue == condition)
{
lastUpdate = currentMax;
}
else
{
int position = currentValue - 1;
if (counters[position] < lastUpdate)
{
counters[position] = lastUpdate + 1;
}
else
{
counters[position]++;
}
if (counters[position] > currentMax)
{
currentMax = counters[position];
}
}
}
for (int i = 0; i < N; i++)
{
if (counters[i] < lastUpdate)
{
counters[i] = lastUpdate;
}
}
return counters;
}

Inspired by Andy's solution, here is a solution in Python that is O(N + M) and gets a score of 100. The key is to avoid the temptation of updating all the counters every time A[K] > 5. Instead you keep track of a global max and reset an individual counter to global max just before you have to increment it. At the end, you set the remaining un-incremented counters to global max. See the comments in the code below:
def solution(N,A):
max = 0
global_max = 0
counters = [0] * N
for operation in A:
if operation > N:
#don't update counters.
#Just keep track of global max until you have to increment one of the counters.
global_max = max
else:
#now update the target counter with global max
if global_max > counters[operation - 1]:
counters[operation - 1] = global_max
#increment the target counter
counters[operation - 1] += 1
#update max after having incremented the counter
if counters[operation - 1] > max:
max = counters[operation - 1]
for i in range(N):
#if any counter is smaller than global max, it means that it was never
#incremented after the global_max was reset. Its value can now be updated
#to global max.
if counters[i] < global_max:
counters[i] = global_max
return counters

Here's a C# solution that gave me 100% score.
The idea is to simply not update the max counters on the spot but rather do it when you actually get to that counter, and then even out any counters that were not set to the max in another loop.
class Solution
{
public int[] solution(int N, int[] A)
{
var result = new int[N];
var latestMax = 0;
var currentMax = 0;
for (int i = 0; i < A.Length; i++)
{
var currentValue = A[i];
if (currentValue >= 1 && currentValue <= N)
{
if (result[currentValue - 1] < currentMax)
{
result[currentValue - 1] = currentMax;
}
result[currentValue - 1]++;
if (result[currentValue - 1] > latestMax)
{
latestMax = result[currentValue - 1];
}
}
else if (currentValue == N + 1)
{
currentMax = latestMax;
}
}
for (int i = 0; i < result.Length; i++)
{
if (result[i] < currentMax)
{
result[i] = currentMax;
}
}
return result;
}
}

Store value from a whileloop into an array then sum the array

I'm trying to store an unknown amount of data into an array, while using a forloop to get data! My task is to find and sum all the numbers form 1 to 1000 that can be divided be 3 and 5.
for (int i = 1; i < 1001; i++)
if (i%3==0)
{
if (i%5==0)
{
//this doesn't work, have tried to convert it to string, didn't work either
int[] array = { i };
//trying to loop the values
for (int j = 0; j < array.Length; i++)
{
//how can I loop this so I dont have to write it all out?
int sum1 = array[j]
}
}
}
Console.ReadKey();

Just because computers can perform repetitive task well doesn't mean you ignore Mathematics. If I got it right, you are trying to find the sum of all the numbers less than 1000 which are divisible by both 3 and 5. So that boils down to all the multiples of 15. Now if you take the floor of 1000/15, you get the the last multiple, which in this case is 66. So, you have to sum the series:
15, 15*2, 15*3,...15*66
=15*(1+2+3+..+66) [15*sum of first 66 positive natural numbers]
=15*66*67/2
So generalizing, finding sum of all numbers less than a and divisible by b is given by:
limit = floor(a/b);
sum = b*limit*(limit+1)/2;

Something like this:
var ListOfInts=new List<int>();
for (int i = 1; i < 1001; i++) {
if (i % 3 == 0 && i % 5 == 0)
ListOfInts.Add(i);
}
var result = ListOfInts.Sum();

Perhaps this code does what you want:
using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
List<int> li = new List<int>();
for (int i = 1; i <= 1000; i++)
{
if (i%3 == 0 && i%5 == 0)
{
li.Add(i);
}
}
Console.Write("sum is " + li.Sum());
Console.ReadLine();
}
}
}

The number devides by 3 and 5 means it devides by 15. So you can start iterating from 15 and incrementing by 15 to skip some iterations:
int sum = 0;
for (int i = 15; i <= 1000; i += 15)
sum += i;

Thanks guys! Alot of good answers, i'm still trying to understand some of them but thanks :)
How come that
List<int> li = new List<int>();
for (int i = 1; i <= 1000; i++)
{
if (i%3 == 0 && i%5 == 0)
{
li.Add(i);
}
}
Console.Write("sum is " + li.Sum());
Console.ReadLine();
give me this
while the code down under
var ListofInts = new List<int>();
for (int i = 0; i < 1001; i++)
{
if (i%3==0 && i%5==0)
{
ListofInts.Add(i);
var result = ListofInts.Sum();
Console.Write(result + ", ");
}
}
gives me this?

A logic issue regarding a very simple solution that performs the factorizing function

This solution factorizes a number (numInput), it works perfectly well except for a logic error I can't seem to find no matter how much I track the solution. The logic error causes the returned result to be 0 no matter the value initialized for numInput.
using System;
namespace factorizer
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine(factorialise());
Console.ReadKey();
}
private static int factorialise()
{
int numInput = int.Parse(Console.ReadLine());
int[] number = new int[numInput];
for (int i = 1; i < numInput; i++) //stores the (n-1)...(n-i) value for the number input'd in the array number[i]
{
number[i - 1] = numInput - i; //the element indicating the index number is 'i - 1' index values start from zero
}
for (int index = 0; index < number.Length; index++) //multiplies the element corresponding the index number with the number input'd
{
numInput = numInput * number[index];
}
return numInput;
}
}
}

Your last item in array stays uninitialized (i.e. equal to zero). Change items count:
int[] number = new int[numInput-1];
Also why not simply use for loop?
int result = 1;
for(int i = 1; i <= numInput; i++)
result *= i;
And another sample just for fun
Enumerable.Range(1, numInput).Aggregate(1, (a,i) => a * i)

How to get specific sequence of array given the array size and the beginning

I have the following case :
a list or array .the size is a variable i get from the user between 1 to 12 .
if the size is 3 then the array {1,2,3}
if the size is 5 then the array {1,2,3,4,5}
and so on
Now the beginning is a variable also.
the sequence i wanna to get is :
if the size 12 for example ,and the beginning is 9 for example
i wanna the following result with this specific order.
9,10,11,12,1,2,3,4,5,6,7,8
I mean i begin with the given beginning until the last item then if the beginning not 1 then i continue with 1 until the beginning.
I did that but it was specific to the size 12:
with this code :
int[] arr = new int[12];
int month = 9;//input from the user
List<int> source = new List<int>();
while (month <= 12)
{
source.Add(month);
month++;
}
if (source.Count < 12)
{
for (int i = 1; i < source[0]; i++)
{
source.Add(i);
}
}
I wanna more general solution to allow variable size not just 12

I have tested it and it works
int arrsize = Convert.ToInt32(Console.ReadLine());
int[] arr = new int[arrsize];
int month = Convert.ToInt32(Console.ReadLine());//input from the user
List<int> source = new List<int>();
while (month <= arrsize)
{
source.Add(month);
month++;
}
if (source.Count < arrsize)
{
for (int i = 1; i < source[0]; i++)
{
source.Add(i);
}
}
foreach (int i in source)
Console.Write(i);
Please add some conditions like array size should not be less than month and user always input integer and do it in try catch for good practice... etc etc
After using some logic from other answers i think below code is much better.
int arrsize = Convert.ToInt32(Console.ReadLine());
int month = Convert.ToInt32(Console.ReadLine());//input from the user
List<int> source = new List<int>();
int temp = 0;
for (int i = 0; i < arrsize; i++)
{
temp = i + month;
if (temp != arrsize)
source.Add(((i + month) % arrsize));
else
source.Add(arrsize);
}
The second method has less complexity only O (n) because it uses only one loop rather 2.
Third Solution is even more simpler :)
for (int i = 0; i < size; i++)
{
if (i < month)
source.Add(i + month);
else
source.Add((i - month) + 1);
}
hope it helps.

How about something like this:
static IEnumerable<int> GetSequence(int size, int beginning)
{
return Enumerable.Range(beginning, size).Select(i => 1 + (i - 1) % 12);
}
You can change the number 12 into a third parameter of the method.

static int[] Sequence(int size, int start)
{
start--;
int[] result = new int[size];
for (int i = 0; i < size; i++)
{
result[i] = ((i + start) % size ) + 1;
}
return result;
}