Wednesday 22 November 2017

C++ Program to Find the Number of Ways to Write a Number as the Sum of Numbers Smaller than Itself


Code:

#include    iostream

using namespace std;

// A function to count all the possible partition.
int CountPartitions(int n)
{
    int p[n], k = 0, count = -1;
p[k] = n;

    // Loop until all the array elements converted to 1 mean no further partition can be generated.
    while(1)
    {
        count++;
        int rem_val = 0;

        // Move the pointer to the index so that p[k] > 1.
        while (k >= 0 && p[k] == 1)
        {
            rem_val += p[k];
k--;
        }
        // If k < 0 then the all the element are broken down to 1.
        if (k < 0)  
            return count;

        // If value greater than 1 is found then decrease it by 1 and increase rem_val to add it to other elements.
        p[k]--;
        rem_val++;

        // Loop until the number of 1's are greater than the value at k index.
        while (rem_val > p[k])
        {
            p[k+1] = p[k];
            // Decrease the rem_val value.
            rem_val = rem_val - p[k];
            k++;
        }

        // Assign the remaining value to the index next to k.
        p[k+1] = rem_val;
        k++;
    }
}

int main()
{
    int n, c;
    cout<<"Enter natural numbers for partition counting: ";
cin>>n;
if (n <= 0)
{
cout<<"Wrong input!!";
return 0;
}

c = CountPartitions(n);
cout<<"The number of partitions of with each element lesser than "<

    return 0;
}


Output:

Case 1:
Enter natural numbers for partition counting: 10
The number of partitions of with each element lesser than 10 is:- 41
 
Case 2:
Enter natural numbers for creating partitions: 50
The number of partitions of with each element lesser than 50 is:- 204225
 
Case 3:
Enter natural numbers for partition counting: 100
The number of partitions of with each element lesser than 100 is:- 190569291



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