回溯算法去重问题的另一种写法，40.组合总和II的java版本

problems/回溯算法去重问题的另一种写法.md

@@ -317,7 +317,38 @@ class Solution {
     }
 }
 ```
+**40.组合总和II**
+```java
+class Solution {
+    List<List<Integer>> result = new ArrayList<>();
+    LinkedList<Integer> path = new LinkedList<>();
+    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
+        Arrays.sort( candidates );
+        if( candidates[0] > target ) return result;
+        backtracking(candidates,target,0,0);
+        return result;
+    }
 
+    public void backtracking(int[] candidates,int target,int sum,int startIndex){
+        if( sum > target )return;
+        if( sum == target ){
+            result.add( new ArrayList<>(path) );
+        }
+        HashSet<Integer> hashSet = new HashSet<>();
+        for( int i = startIndex; i < candidates.length; i++){
+            if( hashSet.contains(candidates[i]) ){
+                continue;
+            }
+            hashSet.add(candidates[i]);
+            path.add(candidates[i]);
+            sum += candidates[i];
+            backtracking(candidates,target,sum,i+1);
+            path.removeLast();
+            sum -= candidates[i];
+        }
+    }
+}
+```
 Python：
 
 **90.子集II**