Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called "Ring Buffer".
One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values.
Your implementation should support following operations:
-
MyCircularQueue(k): Constructor, set the size of the queue to be k. -
Front: Get the front item from the queue. If the queue is empty, return -1. -
Rear: Get the last item from the queue. If the queue is empty, return -1. -
enQueue(value): Insert an element into the circular queue. Return true if the operation is successful. -
deQueue(): Delete an element from the circular queue. Return true if the operation is successful. -
isEmpty(): Checks whether the circular queue is empty or not. -
isFull(): Checks whether the circular queue is full or not.
Example:
MyCircularQueue circularQueue = new MyCircularQueue(3); // set the size to be 3 circularQueue.enQueue(1); // return true circularQueue.enQueue(2); // return true circularQueue.enQueue(3); // return true circularQueue.enQueue(4); // return false, the queue is full circularQueue.Rear(); // return 3 circularQueue.isFull(); // return true circularQueue.deQueue(); // return true circularQueue.enQueue(4); // return true circularQueue.Rear(); // return 4
Note:
- All values will be in the range of [0, 1000].
- The number of operations will be in the range of [1, 1000].
- Please do not use the built-in Queue library.
设计一个环形队列，包含以下几个操作功能：设置队列大小，获取前一个元素，获取最后一个元素，插入一个元素，删除一个元素，判断队列是否满了，判断队列是否为空。不能用内置的Queue函数库。
解法：数组
Java:
class MyCircularQueue {
final int[] a;
int front, rear = -1, len = 0;
public MyCircularQueue(int k) { a = new int[k];}
public boolean enQueue(int val) {
if (!isFull()) {
rear = (rear + 1) % a.length;
a[rear] = val;
len++;
return true;
} else return false;
}
public boolean deQueue() {
if (!isEmpty()) {
front = (front + 1) % a.length;
len--;
return true;
} else return false;
}
public int Front() { return isEmpty() ? -1 : a[front];}
public int Rear() {return isEmpty() ? -1 : a[rear];}
public boolean isEmpty() { return len == 0;}
public boolean isFull() { return len == a.length;}
}
Python:
class Node:
def __init__(self, value):
self.val = value
self.next = self.pre = None
class MyCircularQueue:
def __init__(self, k):
self.size = k
self.curSize = 0
self.head = self.tail = Node(-1)
self.head.next = self.tail
self.tail.pre = self.head
def enQueue(self, value):
if self.curSize < self.size:
node = Node(value)
node.pre = self.tail.pre
node.next = self.tail
node.pre.next = node.next.pre = node
self.curSize += 1
return True
return False
def deQueue(self):
if self.curSize > 0:
node = self.head.next
node.pre.next = node.next
node.next.pre = node.pre
self.curSize -= 1
return True
return False
def Front(self):
return self.head.next.val
def Rear(self):
return self.tail.pre.val
def isEmpty(self):
return self.curSize == 0
def isFull(self):
return self.curSize == self.size
C++:
class MyCircularQueue {
public:
/** Initialize your data structure here. Set the size of the queue to be k. */
MyCircularQueue(int k) {
data.resize(k);
head = 0;
tail = 0;
reset = true;
}
/** Insert an element into the circular queue. Return true if the operation is successful. */
bool enQueue(int value) {
if (isFull()) return false;
// update the reset value when first enqueue happens
if (head == tail && reset) reset = false;
data[tail] = value;
tail = (tail + 1) % data.size();
return true;
}
/** Delete an element from the circular queue. Return true if the operation is successful. */
bool deQueue() {
if (isEmpty()) return false;
head = (head + 1) % data.size();
// update the reset value when last dequeue happens
if (head == tail && !reset) reset = true;
return true;
}
/** Get the front item from the queue. */
int Front() {
if (isEmpty()) return -1;
return data[head];
}
/** Get the last item from the queue. */
int Rear() {
if (isEmpty()) return -1;
return data[(tail + data.size() - 1) % data.size()];
}
/** Checks whether the circular queue is empty or not. */
bool isEmpty() {
if (tail == head && reset) return true;
return false;
}
/** Checks whether the circular queue is full or not. */
bool isFull() {
if (tail == head && !reset) return true;
return false;
}
private:
vector<int> data;
int head;
int tail;
// reset is the mark when the queue is empty
// to differentiate from queue is full
// because in both conditions (tail == head) stands
bool reset;
};
/**
* Your MyCircularQueue object will be instantiated and called as such:
* MyCircularQueue obj = new MyCircularQueue(k);
* bool param_1 = obj.enQueue(value);
* bool param_2 = obj.deQueue();
* int param_3 = obj.Front();
* int param_4 = obj.Rear();
* bool param_5 = obj.isEmpty();
* bool param_6 = obj.isFull();
*/
类似题目：
[LeetCode] 641.Design Circular Deque 设计环形双向队列
All LeetCode Questions List 题目汇总