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Create an Array of Random Numbers whose sum is < X

Posted on 2010-11-20
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Last Modified: 2012-05-10
How would I go about creating a 1 dimensional array with N elements,
whose sum < X?

thx
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Question by:JustinW
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6 Comments
 
LVL 1

Author Comment

by:JustinW
ID: 34180813
and the random numbers are integers between
0 and Z
0
 
LVL 36

Expert Comment

by:Miguel Oz
ID: 34180909
See attached code
public int[] GetRandomArray(int max, int sumMax, int size)
        {
            Debug.Assert(sumMax >= max, "Invalid usage");
            Debug.Assert(max > 0, "Invalid usage");
            Debug.Assert(size > 0, "Invalid usage");
            Random r = new Random();
            List<int> result = new List<int>(size);
            int sum = 0;
            for (int i = 0; i < size; i++)
            {
                result[i] = r.Next(max+1);
                sum = result[i] + sum;
            }
            while (sum > sumMax)
            {
                sum = 0;
                for (int i = 0; i < size; i++)
                {
                    if (result[i] > 0)
                        result[i] = result[i] > 0 ? (result[i] - 1): 0;
                }
            }
            return result.ToArray();
        }

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LVL 36

Accepted Solution

by:
Miguel Oz earned 2000 total points
ID: 34180924
where maxSum = X
maxValue=Z
size=N
public int[] GetRandomArray(int maxValue, int maxSum, int size)
        {
            Debug.Assert(maxSum >= maxValue, "Invalid usage");
            Debug.Assert(maxValue > 0, "Invalid usage");
            Debug.Assert(size > 0, "Invalid usage");
            Random r = new Random();
            List<int> result = new List<int>(size);
            int sum = 0;
            for (int i = 0; i < size; i++)
            {
                result[i] = r.Next(0,maxValue);
                sum = result[i] + sum;
            }
            while (sum > maxSum)
            {
                sum = 0;
                for (int i = 0; i < size; i++)
                {
                    if (result[i] > 0)
                        result[i] = result[i] > 0 ? (result[i] - 1): 0;
                }
            }
            return result.ToArray();
        }

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LVL 1

Author Closing Comment

by:JustinW
ID: 34180934
very nice;
danke
0
 
LVL 1

Author Comment

by:JustinW
ID: 34180941
Here's my crack at it in ruby
def rnd_rng(leng, the_max)
  arr = Array.new(leng){0}
  the_max = rand(the_max)

  i = 0
  while the_max > 0 && i <leng do
    tmp = rand(the_max)
    arr[i] = tmp
    the_max = the_max - tmp
    i +=1
  end

  return arr.shuffle!
end

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LVL 36

Expert Comment

by:Miguel Oz
ID: 34180943
and vb.net version is:
Public Function GetRandomArray(maxValue As Integer, maxSum As Integer, size As Integer) As Integer()
	Debug.Assert(maxSum >= maxValue, "Invalid usage")
	Debug.Assert(maxValue > 0, "Invalid usage")
	Debug.Assert(size > 0, "Invalid usage")
	Dim r As New Random()
	Dim result As New List(Of Integer)(size)
	Dim sum As Integer = 0
	For i As Integer = 0 To size - 1
		result(i) = r.[Next](0, maxValue)
		sum = result(i) + sum
	Next
	While sum > maxSum
		sum = 0
		For i As Integer = 0 To size - 1
			If result(i) > 0 Then
				result(i) = If(result(i) > 0, (result(i) - 1), 0)
			End If
		Next
	End While
	Return result.ToArray()
End Function

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