Update 0216.组合总和III.md

新增java的模板方法

problems/0216.组合总和III.md

@@ -227,6 +227,44 @@ public:
 
 
 Java：
+
+模板方法
+```java
+class Solution {
+	List<List<Integer>> result = new ArrayList<>();
+	LinkedList<Integer> path = new LinkedList<>();
+
+	public List<List<Integer>> combinationSum3(int k, int n) {
+		backTracking(n, k, 1, 0);
+		return result;
+	}
+
+	private void backTracking(int targetSum, int k, int startIndex, int sum) {
+		// 减枝
+		if (sum > targetSum) {
+			return;
+		}
+
+		if (path.size() == k) {
+			if (sum == targetSum) result.add(new ArrayList<>(path));
+			return;
+		}
+		
+		// 减枝 9 - (k - path.size()) + 1
+		for (int i = startIndex; i <= 9 - (k - path.size()) + 1; i++) {
+			path.add(i);
+			sum += i;
+			backTracking(targetSum, k, i + 1, sum);
+			//回溯
+			path.removeLast();
+			//回溯
+			sum -= i;
+		}
+	}
+}
+```
+
+其他方法
 ```java
 class Solution {
     List<List<Integer>> res = new ArrayList<>();