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// 1670. Design Front Middle Back Queue
#include "leetcode.h"
/*
* design a queue that supports 'push' and 'pop' operations in the front,
* middle, and back. notice that when there are two middle position choices, the
* operation is performed on the frontmost middle position choice.
*/
struct node {
int val;
struct node *next;
};
typedef struct {
struct node *front;
struct node *rear;
int cnt;
} FrontMiddleBackQueue;
FrontMiddleBackQueue *frontMiddleBackQueueCreate() {
FrontMiddleBackQueue *q =
(FrontMiddleBackQueue *)malloc(sizeof(FrontMiddleBackQueue));
q->front = NULL;
q->rear = NULL;
q->cnt = 0;
return q;
}
void frontMiddleBackQueuePushFront(FrontMiddleBackQueue *obj, int val) {
struct node *new = (struct node *)malloc(sizeof(struct node));
new->val = val;
new->next = obj->front;
obj->front = new;
if (!obj->rear)
obj->rear = obj->front;
obj->cnt++;
}
void frontMiddleBackQueuePushMiddle(FrontMiddleBackQueue *obj, int val) {
struct node *slow = obj->front;
if (!slow) {
struct node *new = (struct node *)malloc(sizeof(struct node));
new->val = val;
new->next = NULL;
obj->front = new;
obj->rear = new;
obj->cnt++;
} else if (!slow->next) {
struct node *new = (struct node *)malloc(sizeof(struct node));
new->val = val;
obj->front = new;
new->next = slow;
obj->cnt++;
return;
}
struct node *prev_slow = NULL, *fast = obj->front->next;
while (fast) {
prev_slow = slow;
slow = slow->next;
fast = fast->next;
if (fast)
fast = fast->next;
}
struct node *new = (struct node *)malloc(sizeof(struct node));
new->val = val;
prev_slow->next = new;
new->next = slow;
obj->cnt++;
}
void frontMiddleBackQueuePushBack(FrontMiddleBackQueue *obj, int val) {
struct node *new = (struct node *)malloc(sizeof(struct node));
new->val = val;
if (obj->rear)
obj->rear->next = new;
else
obj->front = new;
obj->rear = new;
new->next = NULL;
obj->cnt++;
}
int frontMiddleBackQueuePopFront(FrontMiddleBackQueue *obj) {
if (!obj->front)
return -1;
int res = obj->front->val;
struct node *del = obj->front;
obj->front = obj->front->next;
free(del);
if (!obj->front)
obj->rear = NULL;
obj->cnt--;
return res;
}
int frontMiddleBackQueuePopMiddle(FrontMiddleBackQueue *obj) {
struct node *slow = obj->front;
int res;
if (!slow)
return -1;
if (!slow->next) {
res = slow->val;
obj->front = NULL;
obj->rear = NULL;
obj->cnt--;
free(slow);
return res;
}
struct node *prev_slow = NULL, *prev_prev_slow = NULL,
*fast = obj->front->next;
while (fast) {
prev_prev_slow = prev_slow;
prev_slow = slow;
slow = slow->next;
fast = fast->next;
if (fast)
fast = fast->next;
}
if (!(obj->cnt % 2)) {
res = prev_slow->val;
if (obj->cnt == 2) {
free(prev_slow);
obj->front = slow;
} else {
prev_prev_slow->next = slow;
free(prev_slow);
}
} else {
res = slow->val;
prev_slow->next = slow->next;
free(slow);
}
obj->cnt--;
return res;
}
int frontMiddleBackQueuePopBack(FrontMiddleBackQueue *obj) {
if (!obj->rear)
return -1;
int res = obj->rear->val;
struct node *trav = obj->front;
if (trav == obj->rear) {
obj->front = NULL;
obj->rear = NULL;
free(trav);
} else {
while (trav->next != obj->rear)
trav = trav->next;
trav->next = NULL;
free(obj->rear);
obj->rear = trav;
}
obj->cnt--;
return res;
}
void frontMiddleBackQueueFree(FrontMiddleBackQueue *obj) {
struct node *trav = obj->front, *del = NULL;
while (trav) {
del = trav;
trav = trav->next;
free(del);
}
obj->front = NULL;
obj->rear = NULL;
obj->cnt = 0;
}
int main() {
FrontMiddleBackQueue *obj = frontMiddleBackQueueCreate();
frontMiddleBackQueuePushFront(obj, 1);
frontMiddleBackQueuePushBack(obj, 2);
frontMiddleBackQueuePushMiddle(obj, 3);
frontMiddleBackQueuePushMiddle(obj, 4);
printf("%d\n", frontMiddleBackQueuePopFront(obj)); // expect: 1
printf("%d\n", frontMiddleBackQueuePopMiddle(obj)); // expect: 3
printf("%d\n", frontMiddleBackQueuePopMiddle(obj)); // expect: 4
printf("%d\n", frontMiddleBackQueuePopBack(obj)); // expect: 2
printf("%d\n", frontMiddleBackQueuePopFront(obj)); // expect: -1
frontMiddleBackQueueFree(obj);
}
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