diff --git a/problems/0216.组合总和III.md b/problems/0216.组合总和III.md
index 351b98c9..21230e0f 100644
--- a/problems/0216.组合总和III.md
+++ b/problems/0216.组合总和III.md
@@ -229,24 +229,33 @@ public:
 Java：
 ```java
 class Solution {
-    private List<Integer> path = new ArrayList<>();
-    private List<List<Integer>> res = new ArrayList<>();
+    List<List<Integer>> res = new ArrayList<>();
+    List<Integer> list = new ArrayList<>();
+
     public List<List<Integer>> combinationSum3(int k, int n) {
-        backtracking(k, n, 1);
+        res.clear();
+        list.clear();
+        backtracking(k, n, 9);
         return res;
     }
 
-    private void backtracking (int k, int count, int start) {
-        if (count == 0 && k == 0) {
-            res.add(new ArrayList<>(path));
+    private void backtracking(int k, int n, int maxNum) {
+        if (k == 0 && n == 0) {
+            res.add(new ArrayList<>(list));
             return;
         }
 
-        for (int i = start; i <= 9; i++) {
-            path.add(i);
-            backtracking(k - 1, count - i, i + 1);
-            path.remove(path.size() - 1);
+        // 因为不能重复，并且单个数字最大值是maxNum，所以sum最大值为
+        // （maxNum + (maxNum - 1) + ... + (maxNum - k + 1)） == k * maxNum - k*(k - 1) / 2
+        if (maxNum == 0
+                || n > k * maxNum - k * (k - 1) / 2
+                || n < (1 + k) * k / 2) {
+            return;
         }
+        list.add(maxNum);
+        backtracking(k - 1, n - maxNum, maxNum - 1);
+        list.remove(list.size() - 1);
+        backtracking(k, n, maxNum - 1);
     }
 
 }