C++面试笔试必知必会-队列的实现

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一、环形队列

#include<iostream>
using namespace std;

//环形队列		queue  push pop  front back empty size
class Queue
{
public:
	Queue(int size1=10)
		:cap(size1)
		,front(0)
		,rear(0)
		,size(0)
	{
		pQue = new int[cap];
	}
	~Queue()
	{
		delete[] pQue;
		pQue = nullptr;
	}

public:
	//入队
	void push(int val)
	{
		if ((rear + 1) % cap == front)
		{
			expand(2 * cap);
		}
		pQue[rear] = val;
		rear = (rear + 1)%cap;
		size++;
	}

	//出队
	void pop()
	{
		if (front == rear)
		{
			throw "queue is empty!";
		}
		front = (front + 1) % cap;
		size--;
	}

	//获取队头元素
	int front1()const
	{
		if (front == rear)
		{
			throw "queue is empty!";
		}
		return pQue[front];
	}

	//获取队尾元素
	int rear1()const
	{
		if (front == rear)
		{
			throw "queue is empty!";
		}
		return pQue[(rear - 1 + cap) % cap];
	}
	
	//判断队空
	bool empty()const
	{
		return front == rear;
	}

	//队列元素的个数
	int size1()const
	{
		return size;//	O(n)
		//遍历一遍统计队列元素个数 O(n)
		/*int size = 0;
		for (int i = front; i != rear; i = (i + 1) % cap)
		{
			size++;
		}
		return size;*/
	}
	
private:
	//扩容接口
	void expand(int size)
	{
		int* p = new int[size];
		int i = 0;
		int j = front;
		for (; j != rear; i++, j=(j + 1) % cap)
		{
			p[i] = pQue[j];
		}
		delete[] pQue;
		pQue = p;
		cap = size;
		front = 0;
		rear = i;
	}

private:
	int* pQue;	//存储地址
	int cap;	//容量
	int front;	//队头
	int rear;	//队尾
	int size;	//队元素数量
};

int main() {
	
	int arr[] = { 12,4,56,7,89,31,53,75 };
	Queue q;

	for (int v : arr)
	{
		q.push(v);
	}

	cout << q.front1() << endl;
	cout << q.rear1() << endl;

	q.push(100);
	q.push(200);
	q.push(300);
	q.push(400);

	cout << q.front1() << endl;
	cout << q.rear1() << endl;

	while (!q.empty())
	{
		cout << q.front1() << "  " << q.rear1() << endl;
		q.pop();
	}

	return 0;
}

二、链式队列

#include<iostream>
using namespace std;

//链式队列
class LinkQueue
{
public:
	LinkQueue()
	{
		head = new Node();
		head->next = head;
		head->pre = head;
	}
	~LinkQueue()
	{
		Node* p = head->next;
		while (p != head)
		{
			head->next = p->next;
			p->next->pre = head;//
			delete p;
			p = head->next;
		}
		delete head;
		head = nullptr;
	}

public:
	//入队
	void push(int val)
	{
		Node* s = new Node(val);
		s->next = head;
		s->pre = head->pre;
		head->pre->next = s;
		head->pre = s;
	}

	//出队
	void pop()
	{
		Node* p = head->next;
		head->next = p->next;
		p->next->pre = head;//
		delete p;
	}

	//获取队头元素
	int front()const
	{
		if (head->next == head)
		{
			throw "queue is empty!";
		}
		return head->next->data;
	}

	//获取队尾元素
	int back()const
	{
		if (head->next == head)
		{
			throw "queue is empty!";
		}
		return head->pre->data;
	}

	//判空
	int empty()const
	{
		return head->next == head;
	}

	//


private:
	struct Node
	{
		Node(int data=0)
			:data(data)
			,next(nullptr)
			,pre(nullptr)
		{}
		int data;
		Node* next;
		Node* pre;
	};
	
	Node* head;//指向头节点
};


int main() {
	int arr[] = { 12,4,56,7,89,31,53,75 };
	LinkQueue q;

	for (int v : arr)
	{
		q.push(v);
	}

	cout << q.front() << endl;
	cout << q.back() << endl;

	q.push(100);
	q.push(200);
	q.push(300);
	q.push(400);

	cout << q.front() << endl;
	cout << q.back() << endl;

	while (!q.empty())
	{
		cout << q.front() << "  " << q.back() << endl;
		q.pop();
	}

	return 0;
}

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总结

今天主要给大家实现了，队列的顺序结构和链式结构.