Integer Partition Algorithm

Basic Information of Integer Partition Algorithm

The partition of an integer is a way of writing it as a sum of positive integers. For example, the partitions of the number 5 are:

• 5
• 4 + 1
• 3 + 2
• 2 + 2 + 1
• 2 + 1 + 1 + 1
• 1 + 1 + 1 + 1 + 1

Notice that changing the order of the summands will not create a different partition.

The partition function is inherently recursive in nature since the results of smaller numbers appear as components in the result of a larger number. Let p(n,m) be the number of partitions of n using only positive integers that are less than or equal to m. It may be seen that p(n) = p(n,n), and also p(n,m) = p(n,n) = p(n) for m > n.

Example of Integer Partition Algorithm:

Auxiliary Space: O(n^2)
Time Complexity: O(n(logn))

Implementation of Interger Partition Algorithm in C#

public class IntegerPartition
{
    public static int[,] Result = new int[100,100];

    private static int Partition(int targetNumber, int largestNumber)
    {
        for (int i = 1; i <= targetNumber; i++)
        {
            for (int j = 1; j <= largestNumber; j++)
            {
                if (i - j < 0)
                {
                    Result[i, j] = Result[i, j - 1];
                    continue;
                }
                Result[i, j] = Result[i, j - 1] + Result[i - j, j];
            }
        }
        return Result[targetNumber, largestNumber];
    }

    public static int Main(int number, int target)
    {
        int i;
        for (i = 0; i <= number; i++)
        {
            Result[i, 0] = 0;
        }
        for (i = 1; i <= target; i++)
        {
            Result[0, i] = 1;
        }
        return Partition(number, target);
    }
}