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Deque.c
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Deque.c
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// Deque is a linked list that can be accessed from both ends
// It is a double ended queue
typedef struct node {
int data;
struct node *next;
struct node *prev;
} node;
typedef struct deque {
node *head;
node *tail;
} deque;
void init(deque *d) {
d->head = NULL;
d->tail = NULL;
}
void push_front(deque *d, int data) {
node *new_node = (node *)malloc(sizeof(node));
new_node->data = data;
new_node->next = d->head;
new_node->prev = NULL;
if (d->head != NULL)
d->head->prev = new_node;
d->head = new_node;
if (d->tail == NULL)
d->tail = new_node;
}
void push_back(deque *d, int data) {
node *new_node = (node *)malloc(sizeof(node));
new_node->data = data;
new_node->next = NULL;
new_node->prev = d->tail;
if (d->tail != NULL)
d->tail->next = new_node;
d->tail = new_node;
if (d->head == NULL)
d->head = new_node;
}
int pop_front(deque *d) {
if (d->head == NULL)
return -1;
node *temp = d->head;
int data = temp->data;
d->head = d->head->next;
if (d->head != NULL)
d->head->prev = NULL;
else
d->tail = NULL;
free(temp);
return data;
}
int pop_back(deque *d) {
if (d->tail == NULL)
return -1;
node *temp = d->tail;
int data = temp->data;
d->tail = d->tail->prev;
if (d->tail != NULL)
d->tail->next = NULL;
else
d->head = NULL;
free(temp);
return data;
}
int peek_front(deque *d) {
if (d->head == NULL)
return -1;
return d->head->data;
}
int peek_back(deque *d) {
if (d->tail == NULL)
return -1;
return d->tail->data;
}
int is_empty(deque *d) {
return d->head == NULL;
}