assign groups n choose k java 07-02-2014d1420

2014-08-29

code from
http://stackoverflow.com/questions/15659552/divide-a-group-into-subgroups-of-size-k

code
{
public static void solve(int[] a, int k, int i, List<List<Integer>> subsets) {
    if (i == a.length) {
        for (List<Integer> subset : subsets) {
            System.out.print(subset);               
        }
        System.out.println();
    } else {
        // loop over all subsets and try to put a[i] in
        for (int j = 0; j < subsets.size(); j++) {                 
            if (subsets.get(j).size() < k) {
                // subset j not full
                subsets.get(j).add(a[i]);
                solve(a, k, i+1, subsets); // do recursion
                subsets.get(j).remove((Integer)a[i]);

if (subsets.get(j).size() == 0) {
                     // don't skip empty subsets, so you won't get duplicates
                     break;
                }                    
            }
        }
    }
}
}

usage
{
public static void main(String[] args) {
    int[] a = {1, 2, 3, 4, 5, 6};
    int k = 3;

List<List<Integer>> subsets = new ArrayList<List<Integer>>(a.length / k);
    for (int i = 0; i < a.length / k; i++)
        subsets.add(new ArrayList<Integer>(k));
    solve(a, k, 0, subsets);
}
}

output
{
[1, 2, 3][4, 5, 6]
[1, 2, 4][3, 5, 6]
[1, 2, 5][3, 4, 6]
[1, 2, 6][3, 4, 5]
[1, 3, 4][2, 5, 6]
[1, 3, 5][2, 4, 6]
[1, 3, 6][2, 4, 5]
[1, 4, 5][2, 3, 6]
[1, 4, 6][2, 3, 5]
[1, 5, 6][2, 3, 4]
}

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