added linked list implementation in c++

linked_list/linked_list.cpp

@@ -0,0 +1,188 @@
+#include <iostream>
+
+using namespace std;
+
+class ListNode {
+  public:
+    int val;
+    ListNode* p;
+    
+    ListNode(int passed_val) {
+      val = passed_val;
+      p = nullptr;
+    }
+};
+
+class LinkedList {
+  public:
+    ListNode* head;
+    ListNode* tail;
+    int len;
+    
+    void insert_head(int x) {
+      ListNode* new_head = new ListNode(x);
+      new_head->p = head;
+      head = new_head;
+      len += 1;
+      if (tail == nullptr) {
+        tail = head;
+      }
+    }
+    void insert_tail(int x) {
+      ListNode* new_tail = new ListNode(x);
+      if (tail != nullptr) {
+        tail->p = new_tail;
+      } 
+      tail = new_tail;
+      if (head == nullptr) {
+        head = tail;
+      }
+      len += 1;
+    }
+    void delete_head() {
+      if (head != nullptr) {
+        ListNode* old_head = head;
+        head = head->p;
+        delete old_head;
+        if (head == nullptr) {
+          tail = nullptr;
+        }
+        len -= 1;
+      }
+    }
+    void delete_tail() {
+      if (tail != nullptr) {
+        if (head == tail) {
+          delete head;
+          head = nullptr;
+          tail = nullptr;
+          len = 0;
+        } else {
+          ListNode* current_node = head;
+          ListNode* prev_node = nullptr;
+          while (current_node->p != nullptr) {
+            prev_node = current_node;
+            current_node = current_node->p;
+          }
+          delete tail;
+          tail = prev_node;
+          if (tail != nullptr) {
+            tail->p = nullptr;
+          }
+          len -= 1;
+        }
+      }
+    }
+    void insert_at(int n, int x) {
+      ListNode* new_node = new ListNode(x);
+      ListNode* prev_node = nullptr;
+      ListNode* current_node = head;
+      for (int i = 0; i < n && current_node != nullptr; i++) {
+        prev_node = current_node;
+        current_node = current_node->p;
+      }
+      if (prev_node != nullptr || current_node != nullptr) {
+        prev_node->p = new_node;
+        new_node->p = current_node;
+      }
+      len += 1;
+    }
+    void delete_at(int n) {
+      ListNode* prev_node = nullptr;
+      ListNode* current_node = head;
+      for (int i = 0; i < n; i++) {
+        prev_node = current_node;
+        current_node = current_node->p;
+      }
+      if (current_node != nullptr) {
+        ListNode* next_node = current_node->p;
+        delete current_node;
+        prev_node->p = next_node;
+      }
+      len -= 1;
+    }
+    int get_at(int n) {
+      ListNode* current_node = head;
+      
+      for (int i = 0; i < n && current_node != nullptr; i++) {
+        current_node = current_node->p;
+      }
+
+      if (current_node != nullptr) {
+        return current_node->val;
+      } else {
+        return -1;
+      }
+    }
+    void set_at(int n, int x) {
+      ListNode* current_node = head;
+      
+      for (int i = 0; i < n && current_node != nullptr; i++) {
+        current_node = current_node->p;
+      }
+
+      if (current_node != nullptr) {
+        current_node->val = x;
+      }
+    }
+    void show() {
+      ListNode* current_node = head;
+      
+      cout << "[";
+      if (head == nullptr) {
+        cout << "]";
+      } else {
+        for (int i = 0; i < len && current_node != nullptr; i++) {
+          if (i < len-1) {
+            cout << current_node->val << ", ";
+            current_node = current_node->p;
+          } else {
+            cout << current_node->val << "]";
+          }
+        }
+      }
+      cout << endl;
+    }
+
+    LinkedList() {
+      head = nullptr;
+      tail = head;
+      len = 0;
+    }
+};
+
+int main() {
+  LinkedList ll;
+
+  cout << "initial state of the list" << endl;
+  ll.show();
+  
+  cout << "creating the first version of the list" << endl;
+  ll.insert_tail(12);
+  ll.insert_tail(11);
+  ll.insert_tail(6);
+  ll.insert_tail(27);
+  ll.insert_tail(2);
+  ll.show();
+
+  cout << "deleting the head" << endl;
+  ll.delete_head();
+  ll.show();
+
+  cout << "deleting the tail" << endl;
+  ll.delete_tail();
+  ll.show();
+
+  cout << "inserting at the second position" << endl;
+  ll.insert_at(1, 5);
+  ll.show();
+
+  cout << "the third value" << endl;
+  cout << ll.get_at(2) << endl;
+
+  cout << "setting the third value to 33" << endl;
+  ll.set_at(2, 33);
+  ll.show();
+
+  return 0;
+}