88public class Subsets {
99
1010public static void main (String ...strings ){
11- int []nums =new int []{1 ,2 ,3 };
12- List <List <Integer >>result =subsets (nums );
11+ // int[] nums = new int[]{1,2,3};
12+ int []nums =new int []{1 ,2 ,2 };
13+ List <List <Integer >>result =subsets_backtracking (nums );
1314CommonUtils .printIntegerList (result );
1415 }
1516
@@ -29,5 +30,23 @@ public static List<List<Integer>> subsets(int[] nums) {
2930 }
3031return result ;
3132 }
33+
34+ /**this post: https://discuss.leetcode.com/topic/46159/a-general-approach-to-backtracking-questions-in-java-subsets-permutations-combination-sum-palindrome-partitioning
35+ * is really cool!*/
36+ public static List <List <Integer >>subsets_backtracking (int []nums ) {
37+ List <List <Integer >>result =new ArrayList ();
38+ backtracking (result ,new ArrayList <>(),nums ,0 );
39+ return result ;
40+ }
3241
42+ private static void backtracking (List <List <Integer >>result ,List <Integer >temp ,int []nums ,int start ) {
43+ //ATTN: you'll have to make a new list here before entering the for loop
44+ result .add (new ArrayList (temp ));
45+ for (int i =start ;i <nums .length ;i ++){
46+ if (i !=start &&nums [i ] ==nums [i -1 ])continue ;//add this line here to skip duplicates for Subsets II
47+ temp .add (nums [i ]);
48+ backtracking (result ,temp ,nums ,i +1 );
49+ temp .remove (temp .size ()-1 );
50+ }
51+ }
3352}