[LeetCode] 622.Design Circular Queue 设计环形队列

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();
 */

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