Permutations.java

public class Solution {
    public ArrayList<ArrayList<Integer>> permute(int[] num) {
        // Start typing your Java solution below
        // DO NOT write main() function
       return permutation( num, num.length-1); 
    }
    ArrayList<ArrayList<Integer>> permutation(int [] num, int end)
    {
        ArrayList<ArrayList<Integer>> result=new ArrayList<ArrayList<Integer>> (); 
        if(end<0)
        {
        result.add(new ArrayList<Integer>());
        return result; 
        }
        int rest=num[end]; 
        ArrayList<ArrayList<Integer>> subResult=permutation(num, end-1);
        for(ArrayList<Integer> list: subResult)
        {
            int size=list.size(); 
            for(int i=0; i<=size; i++)
            {
                list.add(i, rest);
                result.add((ArrayList<Integer>)list.clone()); 
                list.remove(i);
            }
        }
        return result; 
    }
}