adding backtracking-2 soln

W6_subsets.py

@@ -0,0 +1,25 @@
+class Solution:
+    def subsets(self, nums: List[int]) -> List[List[int]]:
+        self.result = []
+
+        self.helper(nums, 0, [])
+
+        return self.result 
+
+    def helper(self, nums, pivot, path):
+
+        # Logic
+        self.result.append(list(path))
+
+        for i in range(pivot, len(nums)):
+            # Action
+            path.append(nums[i])
+            # Recurse
+            self.helper(nums, i+1, path)
+            # Backtrack
+            path.pop()
+
+
+# Time complexity: O(n * 2^n)
+# Space complexity: O(n)
+