添加 0090.子集II.md Java版本

problems/0090.子集II.md

@@ -172,7 +172,40 @@ if (i > startIndex && nums[i] == nums[i - 1] ) {
 
 
 Java：
-
+```java
+class Solution {
+   List<List<Integer>> result = new ArrayList<>();// 存放符合条件结果的集合
+   LinkedList<Integer> path = new LinkedList<>();// 用来存放符合条件结果
+   boolean[] used;
+    public List<List<Integer>> subsetsWithDup(int[] nums) {
+        if (nums.length == 0){
+            result.add(path);
+            return result;
+        }
+        Arrays.sort(nums);
+        used = new boolean[nums.length];
+        subsetsWithDupHelper(nums, 0);
+        return result;
+    }
+    
+    private void subsetsWithDupHelper(int[] nums, int startIndex){
+        result.add(new ArrayList<>(path));
+        if (startIndex >= nums.length){
+            return;
+        }
+        for (int i = startIndex; i < nums.length; i++){
+            if (i > 0 && nums[i] == nums[i - 1] && !used[i - 1]){
+                continue;
+            }
+            path.add(nums[i]);
+            used[i] = true;
+            subsetsWithDupHelper(nums, i + 1);
+            path.removeLast();
+            used[i] = false;
+        }
+    }
+}
+```
 
 Python：