232. 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.

這裏定義了一個指向數組的指針和數組容量的最大值MaxSize，如果數組中的數據的個數小於MaxSize，那麼利用指針給數組加上一個數據，如果數組的大小等於MaxSize，那麼所有數據前移一位，在數組最後一位放入新到達的數據。

typedef struct {
    int num;
    int* arr;
    int MaxSize;
} MyQueue;

/** Initialize your data structure here. */
MyQueue* myQueueCreate(int maxSize) {
    MyQueue* queue;
    queue=malloc(sizeof(MyQueue));
    queue->num=0;
    queue->arr=(int*)malloc(sizeof(int)*maxSize);
    queue->MaxSize=maxSize;
    return queue;
}

/** Push element x to the back of queue. */
void myQueuePush(MyQueue* obj, int x) {
    if(obj->num==obj->MaxSize){
        for(int i=0;i<obj->num-1;i++)
           obj->arr[i]=obj->arr[i+1];
      obj->arr[obj->num-1]=x;     
    }
    else{
        obj->arr[obj->num]=x;
        obj->num++;
    }
    
}

/** Removes the element from in front of queue and returns that element. */
int myQueuePop(MyQueue* obj) {
    int p;
    p=obj->arr[0];
    for(int i=0;i<obj->num-1;i++)
    obj->arr[i]=obj->arr[i+1];
    obj->num--;
    return p;
}

/** Get the front element. */
int myQueuePeek(MyQueue* obj) {
    return(obj->arr[0]);
}

/** Returns whether the queue is empty. */
bool myQueueEmpty(MyQueue* obj) {
    return obj->num==0;
}

void myQueueFree(MyQueue* obj) {
    obj->num=0;
}

/**
 * Your MyQueue struct will be instantiated and called as such:
 * struct MyQueue* obj = myQueueCreate(maxSize);
 * myQueuePush(obj, x);
 * int param_2 = myQueuePop(obj);
 * int param_3 = myQueuePeek(obj);
 * bool param_4 = myQueueEmpty(obj);
 * myQueue Free(obj);
 */