组合新增java版本未剪枝优化版本

problems/0077.组合.md

@@ -351,7 +351,30 @@ public:
 
 
 ### Java：
+未剪枝优化
+```java
+class Solution {
+    List<List<Integer>> result= new ArrayList<>();
+    LinkedList<Integer> path = new LinkedList<>();
+    public List<List<Integer>> combine(int n, int k) {
+        backtracking(n,k,1);
+        return result;
+    }
 
+    public void backtracking(int n,int k,int startIndex){
+        if (path.size() == k){
+            result.add(new ArrayList<>(path));
+            return;
+        }
+        for (int i =startIndex;i<=n;i++){
+            path.add(i);
+            backtracking(n,k,i+1);
+            path.removeLast();
+        }
+    }
+}
+```
+剪枝优化：
 ```java
 class Solution {
     List<List<Integer>> result = new ArrayList<>();