Create permutations-II.py

Has to implement DFS in order to operate fast enough to pass the new conditions. 
Uses copy.deepcopy to prevent lists from being retroactively destroyed

permutations-II.py

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+import copy
+class Solution:
+    def permuteUnique(self, nums: List[int]) -> List[List[int]]:
+        res = []
+        nums = sorted(nums)
+        used = [False]*len(nums)
+        li = []
+        self.dfs(nums, used, li, res)
+        return res
+
+    def dfs(self, nums, used, li, res):
+        if len(li) == len(nums):
+            res.append(copy.deepcopy(li))
+            return
+        for i in range(len(nums)):
+            if used[i]:
+                continue
+            if i > 0 and (nums[i] == nums[i-1]) and not used[i-1]:
+                continue
+            used[i] = True
+            li.append(nums[i])
+            self.dfs(nums, used, li, res)
+            used[i] = False
+            li.pop()