LEET code -- Implement Queue using Stacks

 Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

Notes:

• You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
• Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
• You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

用兩個Stack實作

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typedef struct { int *inbox; int *outbox; int inboxsize; int outboxsize; } Queue; /* Create a queue */ void queueCreate(Queue *queue, int maxSize) { //queue = malloc(sizeof(Queue)); queue->inbox=(int *)malloc(sizeof(int)*maxSize); queue->outbox=(int *)malloc(sizeof(int)*maxSize); queue->inboxsize=0; queue->outboxsize=0; } /* Push element x to the back of queue */ void queuePush(Queue *queue, int element) { queue->inbox[queue->inboxsize++]=element; } /* Removes the element from front of queue */ void queuePop(Queue *queue) { if(queue->outboxsize==0){ while(queue->inboxsize!=0){ queue->outbox[(queue->outboxsize)++]=queue->inbox[-- (queue->inboxsize)]; } } return queue->outbox[-- (queue->outboxsize)]; } /* Get the front element */ int queuePeek(Queue *queue) { if(queue->outboxsize==0){ while(queue->inboxsize!=0){ queue->outbox[(queue->outboxsize)++]=queue->inbox[-- (queue->inboxsize)]; } } return queue->outbox[ (queue->outboxsize) -1]; } /* Return whether the queue is empty */ bool queueEmpty(Queue *queue) { if(queue->inboxsize==0 && queue->outboxsize==0 ||queue==NULL)return true; else return false; } /* Destroy the queue */ void queueDestroy(Queue *queue) { //queue=NULL; free(queue->inbox); free(queue->outbox); //free(queue);//out side caller will free }