添加0113.路径总和-ii Java代码

只看到了112题的代码，补上113的

problems/0112.路径总和.md

@@ -347,6 +347,42 @@ class Solution {
 }
 ```
 
+0113.路径总和-ii
+
+```java
+class Solution {
+    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
+        List<List<Integer>> res = new ArrayList<>();
+        if (root == null) return res; // 非空判断
+        
+        List<Integer> path = new LinkedList<>();
+        preorderDFS(root, targetSum, res, path);
+        return res;
+    }
+
+    public void preorderDFS(TreeNode root, int targetSum, List<List<Integer>> res, List<Integer> path) {
+        path.add(root.val);
+        // 遇到了叶子节点
+        if (root.left == null && root.right == null) {
+            // 找到了和为 targetSum 的路径
+            if (targetSum - root.val == 0) {
+                res.add(new ArrayList<>(path));
+            }
+            return; // 如果和不为 targetSum，返回
+        }
+
+        if (root.left != null) {
+            preorderDFS(root.left, targetSum - root.val, res, path);
+            path.remove(path.size() - 1); // 回溯
+        }
+        if (root.right != null) {
+            preorderDFS(root.right, targetSum - root.val, res, path);
+            path.remove(path.size() - 1); // 回溯
+        }
+    }
+}
+```
+
 Python：
 
 0112.路径总和