0112.路径总和.md 添加0113 路径总和II C#代码

problems/0112.路径总和.md

@@ -1523,8 +1523,64 @@ public bool HasPathSum(TreeNode root, int targetSum)
     return HasPathSum(root.left, targetSum - root.val) || HasPathSum(root.right, targetSum - root.val);
 }
 ```
+0113.路径总和：
+```csharp
+/*
+ * @lc app=leetcode id=113 lang=csharp
+ * 0113.路径总和 II
+ * [113] Path Sum II
+ * 递归法
+ */
+public class Solution {
+    private List<List<int>> result = new List<List<int>>();
+    private List<int> path = new List<int>();
 
+    // Main function to find paths with the given sum
+    public IList<IList<int>> PathSum(TreeNode root, int targetSum) {
+        result.Clear();
+        path.Clear();
+        if (root == null) return result.Select(list => list as IList<int>).ToList();
+        path.Add(root.val); // Add the root node to the path
+        traversal(root, targetSum - root.val); // Start the traversal
+        return result.Select(list => list as IList<int>).ToList();
+    }
+
+    // Recursive function to traverse the tree and find paths
+    private void traversal(TreeNode node, int count) {
+        // If a leaf node is reached and the target sum is achieved
+        if (node.left == null && node.right == null && count == 0) {
+            result.Add(new List<int>(path)); // Add a copy of the path to the result
+            return;
+        }
+
+        // If a leaf node is reached and the target sum is not achieved, or if it's not a leaf node
+        if (node.left == null && node.right == null) return;
+
+        // Traverse the left subtree
+        if (node.left != null) {
+            path.Add(node.left.val);
+            count -= node.left.val;
+            traversal(node.left, count);    // Recursive call
+            count += node.left.val;        // Backtrack
+            path.RemoveAt(path.Count - 1); // Backtrack
+        }
+
+        // Traverse the right subtree
+        if (node.right != null) {
+            path.Add(node.right.val);
+            count -= node.right.val;
+            traversal(node.right, count);   // Recursive call
+            count += node.right.val;       // Backtrack
+            path.RemoveAt(path.Count - 1); // Backtrack
+        }
+    }
+}
+
+// @lc code=end
+
+```
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