java - Improve the code of an algorithm of combinations -

i realized algorithm generating combinations. works in following way, if have input:

[a, b, c]

the combinations

[a], [b], [c]. [a, b], [a, c], [b, c], [a, b, c].

while if have in input:

[1,1,2,3]

the combinations be:

[1], [2], [3], [4], [1,2], [1,3], [2,3 ], [1,1,2,3].

however, algorithm has running time of when input list of size 4, if list of size 5 or more program stops , gives me java.lang.outofmemory (i increased memory in java). 1 problem fact have used linkedlist, i'm not sure.

is there better solution?

private list<elemento> combinazionemassima = new arraylist<>(); private log logger = logfactory.getlog(combinazioni3.class);  public combinazioni3(list<elemento> generacombinazionemassima) {     this.combinazionemassima = generacombinazionemassima; }  public void combine() {     this.findallcombinations(combinazionemassima); }  private static class node{     int lastindex = 0; list<elemento> currentlist; public node(int lastindex, list<elemento> list) {         this.lastindex = lastindex;         this.currentlist = list; } public node(node n) {         this.lastindex = n.lastindex;         this.currentlist = new arraylist<elemento>(n.currentlist); } }  public void findallcombinations(list<elemento> combinazioni) {     date datainizio = new date();     list<list<elemento>> resultlist = new arraylist<list<elemento>>();     linkedlist<node> queue = new linkedlist<node>();     int n = combinazioni.size();     arraylist<elemento> temp = new arraylist<elemento>();     temp.add(combinazioni.get(0));     queue.add(new node(0, temp));     // add different integers queue once.     for(int i=1;i<n;++i) {             if(combinazioni.get(i-1) == combinazioni.get(i)) continue;             temp = new arraylist<elemento>();             temp.add(combinazioni.get(i));             queue.add(new node(i, temp));     }     // bfs until have no elements     while(!queue.isempty()) {             node node = queue.remove();             if(node.lastindex+1 < n) {                     node newnode = new node(node);                     newnode.lastindex = node.lastindex+1;                     newnode.currentlist.add(combinazioni.get(node.lastindex+1));                     queue.add(newnode);             }             for(int i=node.lastindex+2;i<n;++i) {                     if(combinazioni.get(i-1) == combinazioni.get(i)) continue;                     // create copy , add integer                     node newnode = new node(node);                     newnode.lastindex = i;                     newnode.currentlist.add(combinazioni.get(i));                     queue.add(newnode);             }             gestoreregole gestoreregole = new gestoreregole();             gestoreregole.esegui(node.currentlist);     }  }