diff --git a/homework4/BiTree.h b/homework4/BiTree.h
index 7065f5f..3abc165 100644
--- a/homework4/BiTree.h
+++ b/homework4/BiTree.h
@@ -4,6 +4,7 @@
 #include <iostream>
 #include <sstream>
 #include <string>
+#include <unordered_map>
 
 template <typename T>
 class BiTree
@@ -17,6 +18,10 @@ public:
     {
     }
 
+    BiTree(char val): data(val), left(nullptr), right(nullptr)
+    {
+    }
+
     static bool is_empty(BiTree* bt)
     {
         if (bt == nullptr)
@@ -96,6 +101,41 @@ public:
         if (right) right->inorderTraversal(oss);
     }
 
+    static BiTree* buildFromPreorderInorderString(const std::string& preorder, const std::string& inorder, int preStart,
+                                                  int preEnd,
+                                                  int inStart, int inEnd, std::unordered_map<char, int>& inMap)
+    {
+        if (preStart > preEnd || inStart > inEnd)
+        {
+            return nullptr;
+        }
+
+        char rootVal = preorder[preStart];
+        BiTree* root = new BiTree(rootVal);
+
+        int inRoot = inMap[rootVal];
+        int leftSubtreeSize = inRoot - inStart;
+
+        root->left = buildFromPreorderInorderString(preorder, inorder, preStart + 1, preStart + leftSubtreeSize,
+                                                    inStart, inRoot - 1, inMap);
+        root->right = buildFromPreorderInorderString(preorder, inorder, preStart + leftSubtreeSize + 1, preEnd,
+                                                     inRoot + 1, inEnd, inMap);
+
+
+        return root;
+    }
+
+    static int getHeight(BiTree* root)
+    {
+        if (root == nullptr)
+        {
+            return 0;
+        }
+        int leftHeight = getHeight(root->left);
+        int rightHeight = getHeight(root->right);
+        return 1 + std::max(leftHeight, rightHeight);
+    }
+
     void toStringHelper(std::ostringstream& oss, const std::string& prefix, bool isLeft, bool hasSibling) const
     {
         if (this != nullptr)
diff --git a/homework4/test3.cpp b/homework4/test3.cpp
index 8af4a80..9112372 100644
--- a/homework4/test3.cpp
+++ b/homework4/test3.cpp
@@ -17,5 +17,25 @@ using namespace std;
 
 int main()
 {
+    int n;
+    cout << "请输入节点个数：";
+    cin >> n;
+
+    string preorder, inorder;
+    cout << "请输入前置索引：" << endl;
+    cin >> preorder;
+    cout << "请输入后置索引：" << endl;
+    cin >> inorder;
+
+    std::unordered_map<char, int> inMap;
+    for (int i = 0; i < inorder.size(); ++i)
+    {
+        inMap[inorder[i]] = i;
+    }
+
+    BiTree<char>* root = BiTree<char>::buildFromPreorderInorderString(preorder, inorder, 0, n - 1, 0, n - 1, inMap);
+
+    cout << "树高为：" << BiTree<char>::getHeight(root) << endl;
+    cout << "该数结构为：" << endl << root->toString() << endl;
     return 0;
-}
\ No newline at end of file
+}