SubsetsII.java

package backtracking;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Created by gouthamvidyapradhan on 14/03/2017.
 Given a collection of integers that might contain duplicates, nums, return all possible subsets.

 Note: The solution set must not contain duplicate subsets.

 For example,
 If nums = [1,2,2], a solution is:

 [
 [2],
 [1],
 [1,2,2],
 [2,2],
 [1,2],
 []
 ]
 */
public class SubsetsII
{
    /**
     * Main method
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception
    {
        int[] n = {1, 2, 3};
        List<List<Integer>> result = new SubsetsII().subsetsWithDup(n);
    }

    public List<List<Integer>> subsetsWithDup(int[] nums)
    {
        List<List<Integer>> result = new ArrayList<>();
        result.add(new ArrayList<>()); //empty subset
        int start = 0, newStart = 0;
        Arrays.sort(nums);
        for(int i = 0, l = nums.length; i < l; i ++)
        {
            newStart = result.size();
            if(i == 0 || nums[i] != nums[i - 1])
            {
                start = 0;
            }
            for(int j = start, resLen = result.size(); j < resLen; j++)
            {
                List<Integer> newList = new ArrayList<>(result.get(j));
                newList.add(nums[i]);
                result.add(newList);
            }
            start = newStart;
        }
        return result;
    }

}