add solution of lab 5

labs/list_implementation/dslist.h

@@ -131,19 +131,32 @@ dslist<T>& dslist<T>::operator= (const dslist<T>& old) {
 
 template <class T>
 void dslist<T>::push_front(const T& v) {
-
-
-
-
-
+  Node<T>* newp = new Node<T>(v);
+  // if list is empty
+  if (!head_) {
+    head_ = newp;
+    tail_ = newp;
+  } else {
+    newp->next_ = head_;
+    head_->prev_ = newp;
+    head_ = newp;
+  }
+  ++size_;
 }
 
 template <class T>
 void dslist<T>::pop_front() {
-
-
-
-
+  assert(head_ != NULL); // list must not be empty
+  Node<T>* temp = head_;
+  head_ = head_->next_;
+  if (head_) {
+    head_->prev_ = NULL;
+  } else {
+    // list becomes empty
+    tail_ = NULL;
+  }
+  delete temp;
+  --size_;
 }
 
 template <class T>
@@ -163,11 +176,17 @@ void dslist<T>::push_back(const T& v) {
 
 template <class T>
 void dslist<T>::pop_back() {
-
-
-
-
-
+  assert(tail_ != NULL); // list must not be empty
+  Node<T>* temp = tail_;
+  tail_ = tail_->prev_;
+  if (tail_) {
+    tail_->next_ = NULL;
+  } else {
+    // list becomes empty
+    head_ = NULL;
+  }
+  delete temp;
+  --size_;
 }
 
 // do these lists look the same (length & contents)?
@@ -186,7 +205,7 @@ bool operator== (dslist<T>& left, dslist<T>& right) {
 
 template <class T>
 bool operator!= (dslist<T>& left, dslist<T>& right){ return !(left==right); }
-template <class T>
+template <class T>
 typename dslist<T>::iterator dslist<T>::erase(iterator itr) {
   assert (size_ > 0);
   --size_;
@@ -256,13 +275,15 @@ void dslist<T>::copy_list(const dslist<T>& old) {
 
 template <class T>
 void dslist<T>::destroy_list() {
-
-
-
-
-
-
-
+  Node<T>* current = head_;
+  while (current) {
+    Node<T>* next = current->next_;
+    delete current;
+    current = next;
+  }
+  head_ = NULL;
+  tail_ = NULL;
+  size_ = 0;
 }
 
 #endif