diff --git a/homework4/BiTree.cpp b/homework4/BiTree.cpp
index e306936..6faab55 100644
--- a/homework4/BiTree.cpp
+++ b/homework4/BiTree.cpp
@@ -1,38 +1,39 @@
 #include "BiTree.h"
+#include <sstream>
 
 bool BiTree::is_empty(BiTree *bt) {
-    if(bt==nullptr) {
+    if (bt == nullptr) {
         return true;
     }
     return false;
 }
 
 bool BiTree::is_leaf(BiTree *bt) {
-    if(bt->left==nullptr && bt->right==nullptr) {
+    if (bt->left == nullptr && bt->right == nullptr) {
         return true;
     }
     return false;
 }
 
 int BiTree::sum_leaf(BiTree *bt) {
-    if(is_empty(bt)) {
+    if (is_empty(bt)) {
         return 0;
     }
-    if(is_leaf(bt)) {
+    if (is_leaf(bt)) {
         return bt->data;
     }
-    return sum_leaf(bt->left)+sum_leaf(bt->right);
+    return sum_leaf(bt->left) + sum_leaf(bt->right);
 }
 
-BiTree* BiTree::createNode(int data) {
-    BiTree* newNode = new BiTree();
+BiTree *BiTree::createNode(int data) {
+    BiTree *newNode = new BiTree();
     newNode->data = data;
     newNode->left = nullptr;
     newNode->right = nullptr;
     return newNode;
 }
 
-void BiTree::insertNode(BiTree*& bt, int value) {
+void BiTree::insertNode(BiTree *&bt, int value) {
     if (bt == nullptr) {
         bt = createNode(value);
     } else {
@@ -42,4 +43,23 @@ void BiTree::insertNode(BiTree*& bt, int value) {
             insertNode(bt->right, value);
         }
     }
-}
\ No newline at end of file
+}
+
+
+void toStringHelper(const BiTree *node, std::ostringstream &oss, const std::string &prefix, bool isLeft) {
+    if (node != nullptr) {
+        oss << prefix;
+
+        oss << (isLeft ? "|--" : "|--") << node->data << "\n";
+
+        std::string newPrefix = prefix + (isLeft ? "|   " : "    ");
+        toStringHelper(node->left, oss, newPrefix, true);
+        toStringHelper(node->right, oss, newPrefix, false);
+    }
+}
+
+std::string BiTree::toString() {
+    std::ostringstream oss;
+    toStringHelper(this, oss, "", false);
+    return oss.str();
+}
diff --git a/homework4/BiTree.h b/homework4/BiTree.h
index 5dd446b..3eca0e0 100644
--- a/homework4/BiTree.h
+++ b/homework4/BiTree.h
@@ -1,6 +1,7 @@
 #ifndef BITREE_H
 #define BITREE_H
 
+#include<sstream>
 
 
 class BiTree {
@@ -10,12 +11,17 @@ public:
     BiTree *right;
 
     static bool is_empty(BiTree *bt);
+
     static bool is_leaf(BiTree *bt);
+
     static int sum_leaf(BiTree *bt);
-    static BiTree* createNode(int data);
-    static void insertNode(BiTree*& bt, int value);
+
+    static BiTree *createNode(int data);
+
+    static void insertNode(BiTree *&bt, int value);
+
+    std::string toString();
 };
 
 
-
 #endif //BITREE_H
diff --git a/homework4/test1.cpp b/homework4/test1.cpp
index 8b68c83..8b19afe 100644
--- a/homework4/test1.cpp
+++ b/homework4/test1.cpp
@@ -1,14 +1,13 @@
 /*
- *二叉树采用二叉链存储结构存放，结点值为int 类型，设计一个递归算法求二叉树 bt 中所有叶子结点值之和
+ *���������ö������洢�ṹ��ţ����ֵΪint ���ͣ����һ���ݹ��㷨������� bt ������Ҷ�ӽ��ֵ֮��
  */
 #include<iostream>
 #include"BiTree.h"
 using namespace std;
 
 
-
-BiTree* createTreeFromArray(const int* values, int size) {
-    BiTree* root = nullptr;
+BiTree *createTreeFromArray(const int *values, int size) {
+    BiTree *root = nullptr;
     for (int i = 0; i < size; ++i) {
         BiTree::insertNode(root, values[i]);
     }
@@ -19,8 +18,9 @@ int main() {
     int testValues[] = {7, 3, 10, 1, 5, 9, 12};
     int size = sizeof(testValues) / sizeof(testValues[0]);
 
-    BiTree* root = createTreeFromArray(testValues, size);
+    BiTree *root = createTreeFromArray(testValues, size);
 
-    cout << "Sum of leaf nodes: " << BiTree::sum_leaf(root) << endl;
+    cout << "���ṹΪ��" << endl << root->toString() << endl;
+    cout << "Ҷ�ӽڵ�֮��Ϊ: " << BiTree::sum_leaf(root) << endl;
     return 0;
-}
\ No newline at end of file
+}