write priority_queue

priority_queue/src/priority_queue.hpp

@@ -9,68 +9,115 @@ namespace sjtu {
 
 /**
  * a container like std::priority_queue which is a heap internal.
+ * Use Skew heap to implement this priority_queue.
  */
-template<typename T, class Compare = std::less<T>>
+template <typename T, class Compare = std::less<T>>
 class priority_queue {
-public:
-	/**
-	 * TODO constructors
-	 */
-	priority_queue() {}
-	priority_queue(const priority_queue &other) {}
-	/**
-	 * TODO deconstructor
-	 */
-	~priority_queue() {}
-	/**
-	 * TODO Assignment operator
-	 */
-	priority_queue &operator=(const priority_queue &other) {}
-	/**
-	 * get the top of the queue.
-	 * @return a reference of the top element.
-	 * throw container_is_empty if empty() returns true;
-	 */
-	const T & top() const {
+  Compare comp;
+  struct Node {
+    T value;
+    Node *left, *right;
+    Node(const T &v) : value(v), left(nullptr), right(nullptr) {}
+  } * root;
+  size_t node_count;
+  void FreeAll(Node *node) {
+    if (node == nullptr) return;
+    FreeAll(node->left);
+    FreeAll(node->right);
+    delete node;
+  }
+  void CopyAll(Node *&dest, Node *src) {
+    if (src == nullptr) return;
+    dest = new Node(src->value);
+    CopyAll(dest->left, src->left);
+    CopyAll(dest->right, src->right);
+  }
 
-	}
-	/**
-	 * TODO
-	 * push new element to the priority queue.
-	 */
-	void push(const T &e) {
+  Node *SkewMerge(Node *a, Node *b) {
+    if (a == nullptr) return b;
+    if (b == nullptr) return a;
+    if (comp(a->value, b->value)) std::swap(a, b);
+    a->right = SkewMerge(a->right, b);
+    std::swap(a->left, a->right);
+    return a;
+  }
 
-	}
-	/**
-	 * TODO
-	 * delete the top element.
-	 * throw container_is_empty if empty() returns true;
-	 */
-	void pop() {
-
-	}
-	/**
-	 * return the number of the elements.
-	 */
-	size_t size() const {
-
-	}
-	/**
-	 * check if the container has at least an element.
-	 * @return true if it is empty, false if it has at least an element.
-	 */
-	bool empty() const {
-
-	}
-	/**
-	 * merge two priority_queues with at most O(logn) complexity.
-	 * clear the other priority_queue.
-	 */
-	void merge(priority_queue &other) {
-
-	}
+ public:
+  priority_queue() : root(nullptr), node_count(0) {}
+  priority_queue(const priority_queue &other) {
+    root = nullptr;
+    CopyAll(root, other.root);
+    node_count = other.node_count;
+  }
+  /**
+   * TODO deconstructor
+   */
+  ~priority_queue() {
+    FreeAll(root);
+    root = nullptr;
+  }
+  /**
+   * TODO Assignment operator
+   */
+  priority_queue &operator=(const priority_queue &other) {
+    if (this == &other) return *this;
+    FreeAll(root);
+    root = nullptr;
+    CopyAll(root, other.root);
+    node_count = other.node_count;
+    return *this;
+  }
+  /**
+   * get the top of the queue.
+   * @return a reference of the top element.
+   * throw container_is_empty if empty() returns true;
+   */
+  const T &top() const {
+    if (empty()) throw container_is_empty();
+    return root->value;
+  }
+  /**
+   * TODO
+   * push new element to the priority queue.
+   */
+  void push(const T &e) {
+    Node *new_node = new Node(e);
+    root = SkewMerge(root, new_node);
+    ++node_count;
+  }
+  /**
+   * TODO
+   * delete the top element.
+   * throw container_is_empty if empty() returns true;
+   */
+  void pop() {
+    if (empty()) throw container_is_empty();
+    Node *old_root = root;
+    root = SkewMerge(root->left, root->right);
+    delete old_root;
+    --node_count;
+  }
+  /**
+   * return the number of the elements.
+   */
+  size_t size() const { return node_count; }
+  /**
+   * check if the container has at least an element.
+   * @return true if it is empty, false if it has at least an element.
+   */
+  bool empty() const { return node_count == 0; }
+  /**
+   * merge two priority_queues with at most O(logn) complexity.
+   * clear the other priority_queue.
+   */
+  void merge(priority_queue &other) {
+    root = SkewMerge(root, other.root);
+    node_count += other.node_count;
+    other.root = nullptr;
+    other.node_count = 0;
+  }
 };
 
-}
+}  // namespace sjtu
 
 #endif