Create Subsets.java

Author: 17tanya

Backtracking/Subsets.java

@@ -0,0 +1,44 @@
+//LeetCode 78. Subsets
+//Question - https://leetcode.com/problems/subsets/
+
+class Solution {
+    public List<List<Integer>> subsets(int[] nums) {
+        List<List<Integer>> res = new ArrayList<>();
+        helper(nums, 0, new ArrayList<>(), res);
+        
+        return res;
+    }
+    
+    public void helper(int nums[], int index, List<Integer> subset, List<List<Integer>> res){
+        res.add(new ArrayList<>(subset));
+        
+        /*
+        For each element we have two choices - 
+            1. Include element in current subset
+            2. Exclude element from current subset
+        
+        We start from index 0 and it considers all elements in the array ==> this leads to the 
+        deepest branch of the state space tree.
+        
+        Each level in the state space tree will signify a subset of different length.
+        
+        Input ==> [1,2,3]
+        Output ==> [[],[1],[1,2],[1,2,3],[1,3],[2],[2,3],[3]]
+        
+        State space tree ==>
+        level 0                                 []
+        level 1             [1]                 [2]                 [3]
+        level 2     [1,2]           [1,3]      [2,3]
+        level 3    [1,2,3]
+        */
+        
+        for(int i = index ; i < nums.length ; i++){
+            //Choice 1. Include the elment
+            subset.add(nums[i]);
+            helper(nums, i + 1, subset, res);
+            //Choice 2. Exclude the element ==> Basically Backtrack after choosing the element
+            subset.remove(subset.size()-1);
+        }
+        
+    }
+}