[回溯算法去重问题的另一种写法.md] add python code

Author: haofengsiji

problems/回溯算法去重问题的另一种写法.md

@@ -250,9 +250,84 @@ used数组可是全局变量，每层与每层之间公用一个used数组，所
 
 Java：
 
-
 Python：
 
+**90.子集II**
+
+```python
+class Solution:
+    def subsetsWithDup(self, nums: List[int]) -> List[List[int]]:
+        res = []
+        nums.sort()
+        def backtracking(start, path):
+            res.append(path)
+            uset = set()
+            for i in range(start, len(nums)):
+                if nums[i] not in uset:
+                    backtracking(i + 1, path + [nums[i]])
+                    uset.add(nums[i])
+
+        backtracking(0, [])
+        return res
+```
+
+**40. 组合总和 II**
+
+```python
+class Solution:
+    def combinationSum2(self, candidates: List[int], target: int) -> List[List[int]]:
+        
+        res = []
+        candidates.sort()
+
+        def backtracking(start, path):
+            if sum(path) == target:
+                res.append(path)
+            elif sum(path) < target:
+                used = set()
+                for i in range(start, len(candidates)):
+                    if candidates[i] in used:
+                        continue
+                    else:
+                        used.add(candidates[i])
+                        backtracking(i + 1, path + [candidates[i]])
+        
+        backtracking(0, [])
+
+        return res
+```
+
+**47. 全排列 II**
+
+```python
+class Solution:
+    def permuteUnique(self, nums: List[int]) -> List[List[int]]:
+        path = []
+        res = []
+        used = [False]*len(nums)
+
+        def backtracking():
+            if len(path) == len(nums):
+                res.append(path.copy())
+            
+            deduplicate = set()
+            for i, num in enumerate(nums):
+                if used[i] == True:
+                    continue
+                if num in deduplicate:
+                    continue
+                used[i] = True
+                path.append(nums[i])
+                backtracking()
+                used[i] = False
+                path.pop()
+                deduplicate.add(num)
+        
+        backtracking()
+
+        return res
+```
+
 
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