C++ Prime确实有点难啊!看了好久都没弄清楚,一点点慢慢来。
#include <iostream> #include <string> #include <cstdio> template <class Type> class Queue; //function template declaration must precede friend declaration in QueueItem template <class T> std::ostream& operator<<(std::ostream&,const Queue<T>&); template <class Type> class QueueItem{ friend class Queue<Type>; // needs access to item and next friend std::ostream& operator<< <Type> (std::ostream&,const Queue<Type>&); // private class: no public section QueueItem(const Type &t):item(t),next(0){} Type item; // value stored in this element QueueItem *next; // pointer to next element in the Queue }; template <class Type> class Queue{ // needs access to head friend std::ostream& operator << <Type> (std::ostream&,const Queue<Type>&); public: // empty Queue Queue():head(0),tail(0){} // construct a Queue from a pair of iterators on some sequence template <class It> Queue(It beg,It end): head(0),tail(0){ copy_elems(beg,end); } // copy control to manage pointers to QueueItems in the Queue Queue(const Queue &Q) :head(0),tail(0){ copy_elems(Q); } Queue& operator=(const Queue&); // left as exercise for the reader ~Queue() { destroy(); } // replace current Queue by contents delimited by a pair of iterators template <class Iter> void assign(Iter,Iter); // return element from head of Queue // unchecked operation:front on an empty Queue is undefined Type& front() {return head->item; } const Type &front() const {return head->item;} void push(const Type &); void pop(); bool empty()const{ //true if no elements in the Queue return head == 0; } private: QueueItem<Type> *head; QueueItem<Type> *tail; void destroy(); void copy_elems(const Queue&); // version of copyto be used by assign to copy elements from iterator range template <class Iter> void copy_elems(Iter,Iter); }; // push 函数 // push 成员将新项放在队列末尾 template <class Type> void Queue<Type>::push(const Type &val) { // allocate a new QueueItem object QueueItem<Type> *pt = new QueueItem<Type>(val); // put item onto existing(目前) queue if(empty()) head = tail = pt; // the queue now has only one element else { tail->next = pt; // add new element to end of the queue tail = pt; } } //copy_element 函数 template <class Type> void Queue<Type>::copy_elems(const Queue &orig) { // copy elements from orig into this Queue // loop stops when to pt == 0, which happens when we reach orig.tail for (QueueItem<Type> *pt = orig.head; pt; pt = pt->next) push(pt->item); // copy element } // destroy 函数 template <class Type> void Queue<Type>::destroy() { while (!empty()) pop(); } //pop函数 template <class Type> void Queue<Type>::pop() { // pop is unchecked: Popping off an empty Queue is undefined QueueItem<Type>* p = head; head = head->next; delete p; } int main() { int n,val; Queue<int> IntQ; /*Queue<double> DouQ; Queue<string> StrQ;*/ printf("Please enter you want total number: "); std::cin>>n; while(n){ std::cin>>val; IntQ.push(val); n--; } while(!IntQ.empty()){ std::cout<<IntQ.front()<<std::endl; IntQ.pop(); } return 0; }
时间: 2024-10-13 12:16:56