From 2d4a07579ef2200ee9f372546ecb77e963a0253e Mon Sep 17 00:00:00 2001
From: gaoyuankan <kangaoyuan@163.com>
Date: Fri, 28 Feb 2025 18:00:39 +0800
Subject: [PATCH] Finish hw02

---
 .gitignore |  1 +
 main.cpp   | 83 +++++++++++++++++++++++++++++++++++++++---------------
 2 files changed, 62 insertions(+), 22 deletions(-)

diff --git a/.gitignore b/.gitignore
index 9ed92a0..8d87ec4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
+tags
 build
 GNUmakefile
diff --git a/main.cpp b/main.cpp
index dc25c6b..e7ed251 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,33 +1,38 @@
 /* 基于智能指针实现双向链表 */
 #include <cstdio>
-#include <memory>
+#include <memory> // For three smart pointers
+#include <cassert> // It's a invaluable thing
 
-struct Node {
+// Actually, we need public inherit
+struct Node : std::enable_shared_from_this<Node> {
+    int value;
     // 这两个指针会造成什么问题？请修复
+    // Obviously, it will cause cycle reference
     std::shared_ptr<Node> next;
-    std::shared_ptr<Node> prev;
+    std::weak_ptr<Node> prev;
     // 如果能改成 unique_ptr 就更好了!
-
-    int value;
+    // We can do this from another branch.
 
     // 这个构造函数有什么可以改进的？
-    Node(int val) {
-        value = val;
+    // Explicit and Initializer list
+    explicit Node(int val) : value(val) {
+        /*
+         *value = val;
+         */
     }
 
     void insert(int val) {
         auto node = std::make_shared<Node>(val);
         node->next = next;
-        node->prev = prev;
-        if (prev)
-            prev->next = node;
-        if (next)
+        node->prev = shared_from_this();
+        if(next)
             next->prev = node;
+        next = node;
     }
 
     void erase() {
-        if (prev)
-            prev->next = next;
+        if (prev.lock())
+            prev.lock()->next = next;
         if (next)
             next->prev = prev;
     }
@@ -43,17 +48,44 @@ struct List {
     List() = default;
 
     List(List const &other) {
-        printf("List 被拷贝！\n");
-        head = other.head;  // 这是浅拷贝！
+        printf("List copy constructor！\n");
+        /*
+         *head = other.head;  // 这是浅拷贝！
+         */
         // 请实现拷贝构造函数为 **深拷贝**
+        auto origin_head = other.head;
+        if(!origin_head)
+            return;
+
+        auto current_head = std::make_shared<Node>(origin_head->value); 
+        auto result = current_head;
+        origin_head = origin_head->next;
+        while(origin_head){
+        //while(origin_head.get()){
+            current_head->insert(origin_head->value);
+            origin_head = origin_head->next; 
+            current_head = current_head->next;
+        }
+        // Inside constructor, there is no content before, so it's redundant.
+        // You can see the content of front()
+        assert(!front());
+        printf("front() == %p\n", front());
+        for (auto cur = front(); cur; ) {
+            auto tmp = cur;
+            cur = cur->next.get();
+            delete tmp;
+        }
+        head = result;
     }
 
+    // From this source file context, there is no lvalue assignment copy action.
     List &operator=(List const &) = delete;  // 为什么删除拷贝赋值函数也不出错？
 
+    // Move sementics
     List(List &&) = default;
     List &operator=(List &&) = default;
 
-    Node *front() const {
+    Node* front() const {
         return head.get();
     }
 
@@ -72,6 +104,7 @@ struct List {
     }
 
     Node *at(size_t index) const {
+        // auto is Node*
         auto curr = front();
         for (size_t i = 0; i < index; i++) {
             curr = curr->next.get();
@@ -80,10 +113,10 @@ struct List {
     }
 };
 
-void print(List lst) {  // 有什么值得改进的？
+void print(const List& lst) {  // 有什么值得改进的？
     printf("[");
-    for (auto curr = lst.front(); curr; curr = curr->next.get()) {
-        printf(" %d", curr->value);
+    for (auto cur = lst.front(); cur; cur = cur->next.get()) {
+        printf(" %d", cur->value);
     }
     printf(" ]\n");
 }
@@ -98,18 +131,24 @@ int main() {
     a.push_front(9);
     a.push_front(4);
     a.push_front(1);
+    a.push_front(9);
 
-    print(a);   // [ 1 4 9 2 8 5 7 ]
+    print(a);   // [9 1 4 9 2 8 5 7]
 
+    a.pop_front();
+    print(a);   // [1 4 9 2 8 5 7]
+                
     a.at(2)->erase();
-
     print(a);   // [ 1 4 2 8 5 7 ]
 
     List b = a;
 
     a.at(3)->erase();
-
     print(a);   // [ 1 4 2 5 7 ]
+
+    a.at(3)->insert(10);
+    print(a);   // [ 1 4 2 5 10 7 ]
+
     print(b);   // [ 1 4 2 8 5 7 ]
 
     b = {};