How to loop random number to make result equal user input summary

Question

i have some problem like this. user(A) enter 500000 to my application and then i want to generate 50 random 5 digit number and when summary 50 random number need to equal 500000, How to do like i tried already but it's not working this is my code

            int balane = 500000;
            int nums = 50;
            int max = balane / nums;
            Random rand = new Random();
            int newNum = 0;
            int[] ar = new int[nums];
            for (int i = 0; i < nums - 1; i++)
            {
                newNum = rand.Next(max);
                ar[i] = newNum;
                balane -= newNum;
                max = balane / (nums - i - 1);

                ar[nums - 1] = balane;
            }

            int check = 0;
            foreach (int x in ar)
            {
                check += x;
            }

the result that i tell you not working because in my array list i have value more than 5 digit but the result equal 500000.

How to solve this issue ? Thank you very much.

The screenshot you've shown isn't the same as the code you've posted. The screenshot uses `rand.Next(0, 99999)` whereas the code you've posted as text uses `rand.Next(0, max)`. The code that uses `rand.Next(0, max)` works. (Admittedly I'd only allocate `ar[num -1]` after the loop, but that's a different matter. — Jon Skeet, Jun 16 '18 at 08:06
@user3001046 - Do you mean you want 50 random numbers that sum to 500,000? — Enigmativity, Jun 16 '18 at 08:25
Right, so at this point it's a matter of your algorithm being broken. Consider that `rand.Next(max)` could always return 0... at that point, your final element would have to be the original target. You need to think about applying a minimum as well as a maximum. Note that your question would be better (IMO) if you'd remove the screenshot, add a `Console.WriteLine(ar[nums - 1])` after the loop, and just include the output of that. There's no need for an image here. — Jon Skeet, Jun 16 '18 at 08:36
https://stackoverflow.com/questions/50876175/how-to-generate-random-5-digit-number-depend-on-user-summary why are you posting same question again ? — Amit, Jun 16 '18 at 08:48
@paparazzo is duplicate but this question can make you understand me — user3001046, Jun 16 '18 at 09:24
@user3001046 update the original question if you need to, but posting a duplicate question is against the rules. — cwharris, Jun 16 '18 at 13:38

mrbm · Accepted Answer · 2018-06-16T10:15:22.157

This works for me

    public static void test(int balance = 500000, int nums = 50, int max_digits = 5)
    {
        int rest = balance;
        var max_value = (int)Math.Pow(10, max_digits) - 1;

        var rand = new Random();

        int[] ar = new int[nums];
        for (int i = 0; i < nums - 1; i++)
        {
            var max = rest / (nums - i);
            if (max > max_value) max = max_value;
            var newNum = rand.Next(max);
            ar[i] = newNum;
            rest -= newNum;
        }
        while (rest > max_value)
        {
            var all_values_are_max = true;
            for (int i = 0; i < nums - 1; i++)
            {
                if (ar[i] < max_value)
                {
                    var d = (int)((max_value - ar[i]) / 10.0); // 10% increase
                    ar[i] += d;
                    rest -= d;
                    all_values_are_max = false;
                }
            }
            if (all_values_are_max)
                throw new Exception("This is not possible at all!");
        }
        while (rest < 0)
        {
            for (int i = 0; i < nums - 1; i++)
            {
                if (ar[i] > 0)
                {
                    var d = (int)(ar[i] / 20.0); // %5 decrease
                    ar[i] -= d;
                    rest += d;
                }
            }
        }
        ar[nums - 1] = rest;

        int check_sum = 0;
        foreach (int x in ar)
        {
            check_sum += x;
            if (x > max_value || x < 0)
                MessageBox.Show("wrong value");
        }
        if (check_sum != balance)
            MessageBox.Show("Error: sum is " + check_sum);

        MessageBox.Show("ok");
    }

For example, test(500000,50) works fine all times, but test(500000, 5) throw an exception, because is not possible

This question is an exact duplicate from the same user. Please move this answer to that question to discourage duplicate posting. — cwharris, Jun 16 '18 at 13:40

Enigmativity · Answer 2 · 2018-06-16T13:28:43.840

0

Perhaps try this:

var rnd = new Random();

var numbers = Enumerable.Range(0, 50).Select(x => rnd.Next(500_000)).OrderBy(x => x).ToArray();

numbers = numbers.Skip(1).Zip(numbers, (x1, x0) => x1 - x0).ToArray();

numbers = numbers.Append(500_000 - numbers.Sum()).ToArray();

Console.WriteLine(numbers.Count());
Console.WriteLine(numbers.Sum());

This outputs:

50
500000

This works by generating 50 random numbers between 0 and 499,999 inclusively. It then sorts them ascendingly and then gets the difference between each successive pair. This by definition produces a set of 49 values that almost adds up to 500,000. It's then just a matter of adding the one missing number by doing 500_000 - numbers.Sum().

edited Jun 16 '18 at 13:28

answered Jun 16 '18 at 12:53

Enigmativity

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This question is an exact duplicate from the same user. Please move this answer to that question to discourage duplicate posting. – cwharris Jun 16 '18 at 13:39
1

@cwharris - Done and I closed this question. – Enigmativity Jun 17 '18 at 00:28

How to loop random number to make result equal user input summary

2 Answers2