Every possible combination of X split into N stacks

问题

I am sure this problem has a formal name, and knowing that name would probably help me find the solution, but I don't know it, and wording the problem for Google keeps pointing me to the Knapsack Problem, which isn't the same thing.

I want to take some value X and find every possible combination of splitting that value into N stacks of whole integers.

In case my wording is confusing, here is an example of X = 4, N = 3

Stack -> 1 | 2 | 3 |
----------------------
#1-----> 4 | 0 | 0 |
----------------------
#2-----> 3 | 1 | 0 |
----------------------
#3-----> 2 | 1 | 1 |
----------------------
#4-----> 2 | 2 | 0 |

Duplication is acceptable, since its easy to remove, but ideally it would not be calculated. An algorithm for solving the problem would be perfect, but even finding out of the problem has a name would make research easier. Thanks.

回答1:

This is user434507's answer in C#:

class Program
{
    static void Main(string[] args)
    {
        var v = Partitions(5, 3, 5);

        for (int i = 0; i < v.Count; i++)
        {
            for (int x = 0; x < v[i].Count; x++)
                Console.Write(v[i][x] + " "); 
            Console.WriteLine();
        }
    }

    static private List<List<int>> Partitions(int total, int stacks, int max)
    {
        List<List<int>> partitions = new List<List<int>>();

        if (total <= 1 || stacks == 1)
        {
            if (total <= max)
            {
                partitions.Add(new List<int>());
                partitions[0].Add(total);
            }

            return partitions;
        }
        for (int y = Math.Min(total, max); y >= 1; y--)
        {
            var w = Partitions(total - y, stacks - 1, y);
            for (int i = 0; i < w.Count; i++)
            {
                w[i].Add(y);
                partitions.Add(w[i]);
            }
        }

        return partitions;
    }
}

回答2:

These are in fact integer partitions as a deleted answer remarks. Using Mathematica:

IntegerPartitions[4, 3] // PadRight //Grid

Output:

I could not find a C# implementation but here are a couple of related questions:

Elegant Python code for Integer Partitioning

Integer Partition in Java

Algorithm for generating integer partitions

Google hits:

Integer Partition Algorithm by Jerome Kelleher

Integer Partition Algorithm by Daniel Scocco

Fast Algorithms for Generating Integer Partitions (PDF) (looks heavy-duty)

Stony Brook Algorithm Repository - Partitions

回答3:

This seems to do the trick:

vector<vector<int> > partitions(int X, int N, int Y)
{
    vector<vector<int> > v;
    if(X<=1 || N==1)
    {
        if(X<=Y)
        {
            v.resize(1);
            v[0].push_back(X);
        }
        return v;
    }
    for(int y=min(X, Y); y>=1; y--)
    {
        vector<vector<int> > w = partitions(X-y, N-1, y);
        for(int i=0; i<w.size(); i++)
        {
          w[i].push_back(y);
          v.push_back(w[i]);
        }
    }
    return v;


   }

int main()
{
    vector<vector<int> > v = partitions(5, 3, 5);
    int i;
    for(i=0; i<v.size(); i++)
    {
        int x;
        for(x=0; x<v[i].size(); x++)
            printf("%d ", v[i][x]);
        printf("\n");
    }
    return 0;
}

来源：https://stackoverflow.com/questions/11019574/every-possible-combination-of-x-split-into-n-stacks

标签

algorithm

math

combinatorics