133 lines
2.2 KiB
C++
133 lines
2.2 KiB
C++
/**
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* @file queue.h
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*
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* A first-in first-out queue.
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*/
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#ifndef COL_QUEUE_H
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#define COL_QUEUE_H
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/**
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* A FIFO queue.
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*
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* Based on a singly linked list with a tail pointer.
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*
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* TODO: A double-ended array-based queue would be faster.
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*/
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template<typename T>
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class Queue {
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FORBID_ACCIDENTAL_COPIES(Queue); // No copy constructor defined (yet)
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private:
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struct Node {
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T data;
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Node *next;
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Node() : next(NULL) { }
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Node(const T& value) : data(value), next(NULL) {}
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};
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private:
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Node *head_;
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Node **tailp_;
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public:
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Queue() { DEBUG_POISON_PTR(tailp_); }
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~Queue() {
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Clear();
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}
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/**
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* Creates an empty queue.
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*/
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void Init() {
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head_ = NULL;
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tailp_ = &head_;
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}
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/**
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* Adds an element to the tail end of the queue, but not initializing it.
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*
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* @return a pointer to the default-constructed but uninitialized value
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*/
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T *Add() {
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Node *node = new Node();
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*tailp_ = node;
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tailp_ = &node->next;
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return &node->data;
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}
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/**
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* Adds the specified element to the tail end.
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*
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* @return a pointer to the tail end, which contains the given parameter
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*/
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T *Add(const T& value) {
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Node *node = new Node(value);
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node->next = NULL;
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*tailp_ = node;
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tailp_ = &node->next;
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return &node->data;
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}
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/**
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* Pops from the head of the queue, not returning anything.
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*/
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void PopOnly() {
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Node *tmp = head_;
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head_ = head_->next;
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delete tmp;
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if (unlikely(head_ == NULL)) {
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tailp_ = &head_;
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}
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}
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/**
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* Pops from the head of the queue, returning a copy of the item.
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*/
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T Pop() {
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T val(head_->data);
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PopOnly();
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return val;
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}
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/**
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* Determines if the queue is empty.
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*/
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bool is_empty() const {
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return head_ == NULL;
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}
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/**
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* Gets the element at the head of the queue.
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*/
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const T& top() const {
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return head_->data;
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}
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/**
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* Gets the element at the head of the queue.
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*/
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T& top() {
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return head_->data;
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}
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/**
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* Clears all elements from the queue.
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*/
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void Clear() {
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Node *cur;
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Node *next;
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for (cur = head_; cur; cur = next) {
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next = cur->next;
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delete cur;
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}
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head_ = NULL;
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tailp_ = &head_;
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}
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};
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#endif
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