Double ended queue

deque It's a double ended queue
（deque, full name double-ended queue） It's a data structure with the properties of queue and stack . Elements in a two terminal queue can pop up from both ends , It limits the insertion and deletion operations on both sides of the table .
Structure definition and initialization

typedef int T;
typedef struct DoubleQuene
{
    
	T data[MAXSIZE];
	int front;// Head position 
	int rear;// Tail position 
}*deque;

bool InitQuene(deque q)// initialization 
{
    
	if (!q)
		return false;
	q->front = 0;
	q->rear = 0;
	return true;
}

Compared with circular queues , There are functions equivalent to header insertion and tail deletion .

bool push_back(deque q, T val)// Join the team from the end 
{
    
	if (Is_Full(q))
		return false;
	q->data[q->rear] = val;
	q->rear = (q->rear + 1) % MAXSIZE;
	return true;
}

bool push_front(deque q, T val)// Join the team from scratch 
{
    
	if (Is_Full(q))
		return false;
	q->front = (q->front + MAXSIZE - 1) % MAXSIZE;
	q->data[q->front] = val;
	return true;
}

T pop_front(deque q)// Out of the team 
{
    
	if (Is_Empty(q))
		return -1;
	T tmp = q->data[q->front];
	q->front = (q->front + 1) % MAXSIZE;
	return tmp;
}

T pop_back(deque q)// Join the team from the end 
{
    
	if (Is_Empty(q))
		return -1;
	q->rear = (q->rear + MAXSIZE - 1) % MAXSIZE;
	T tmp = q->data[q->rear];
	return tmp;
}

There is also getting the head and tail elements .

T GetHead(deque q)// Get team leader elements 
{
    
	if (Is_Empty(q))
		return -1;
	return q->data[q->front];
}

T GetTail(deque q)// Get the tail node 
{
    
	if (Is_Empty(q))
		return -1;
	return q->data[q->front];
}

Other operations

bool ClearQuene(deque q)// Qingdui 
{
    
	if (!q)
		return false;
	q->front = q->rear = 0;
	return true;
}

bool Is_Empty(deque q)// Sentenced to empty 
{
    
	return q->front == q->rear;
}

bool Is_Full(deque q)// Full sentence 
{
    
	return (q->rear + 1) % MAXSIZE == q->front;
}

int GetLength(deque q)// The number of data 
{
    
	return (q->rear - q->front + MAXSIZE) % MAXSIZE;
}

All the code

#include <stdio.h>
#include <malloc.h>

#define MAXSIZE 40

typedef int T;

typedef struct DoubleQuene
{
    
	T data[MAXSIZE];
	int front;// Head position 
	int rear;// Tail position 
}*deque;

bool InitQuene(deque q)// initialization 
{
    
	if (!q)
		return false;
	q->front = 0;
	q->rear = 0;
	return true;
}

bool ClearQuene(deque q)// Qingdui 
{
    
	if (!q)
		return false;
	q->front = q->rear = 0;
	return true;
}

bool Is_Empty(deque q)// Sentenced to empty 
{
    
	return q->front == q->rear;
}

bool Is_Full(deque q)// Full sentence 
{
    
	return (q->rear + 1) % MAXSIZE == q->front;
}

int GetLength(deque q)// The number of data 
{
    
	return (q->rear - q->front + MAXSIZE) % MAXSIZE;
}

T GetHead(deque q)// Get team leader elements 
{
    
	if (Is_Empty(q))
		return -1;
	return q->data[q->front];
}

T GetTail(deque q)// Get the tail node 
{
    
	if (Is_Empty(q))
		return -1;
	return q->data[q->front];
}

bool push_back(deque q, T val)// Join the team from the end 
{
    
	if (Is_Full(q))
		return false;
	q->data[q->rear] = val;
	q->rear = (q->rear + 1) % MAXSIZE;
	return true;
}

bool push_front(deque q, T val)// Join the team from scratch 
{
    
	if (Is_Full(q))
		return false;
	q->front = (q->front + MAXSIZE - 1) % MAXSIZE;
	q->data[q->front] = val;
	return true;
}

T pop_front(deque q)// Out of the team 
{
    
	if (Is_Empty(q))
		return -1;
	T tmp = q->data[q->front];
	q->front = (q->front + 1) % MAXSIZE;
	return tmp;
}

T pop_back(deque q)// Join the team from the end 
{
    
	if (Is_Empty(q))
		return -1;
	q->rear = (q->rear + MAXSIZE - 1) % MAXSIZE;
	T tmp = q->data[q->rear];
	return tmp;
}

void Show(deque q)// Traverse 
{
    
	if (Is_Empty(q))
		return;
	int i = q->front;
	while (i != q->rear)
	{
    
		printf("%d ", q->data[i]);
		i = (i + 1) % MAXSIZE;
	}
	printf("\n");
}

int main()
{
    
	deque q;
	q = (deque)malloc(sizeof(DoubleQuene));
	InitQuene(q);
	for (int i = 1; i <= 10; i++)
	{
    
		push_front(q, i);
		push_back(q,i);
	}
	Show(q);
	printf("Head:%d\n", GetHead(q));
	printf("Tail:%d\n", GetTail(q));
	printf("Len:%d\n", GetLength(q));
	for (int i = 1; i <= 3; i++)
	{
    
		printf("%d ", pop_front(q));
		printf("%d ", pop_back(q));
	}
	printf("\n");
	Show(q);
	return 0;
}

Double ended queues can complete the desired functions by limiting the interface , For example, limit tail insertion , Tail deletion is used as a stack, and so on .