Circular queue
1. Basic understanding of circular queue
2. Concrete realization
- Implement circular queue with array
2.1 Join the team
- Ideas:
- Also judge whether it is full
- The added element is added to the position of the rear, and then the rear moves to the back. Originally, it only needs to be added, but it is a circular queue. The next one of the last is the subscript 0, so the modulo operation is used;
//入队
public boolean enQueue(int value) {
//1.先判断是否为满
if(isFull()){
return false;
}
this.elem[rear] = value;
rear = (rear+1)%this.elem.length;
return true;
}
2.2 Departure
- Ideas:
- First determine whether it is empty
- Out directly from the front of the team;
public boolean deQueue() {
//1.判断是否为空
if(isEmpty()){
return false;
}
front = (front+1)%elem.length;
return true;
}
2.3 Get the head element
- Idea: Because it is implemented with an array, just return the element of the head subscript directly;
public int Front() {
//1.判断是否为空
if(isEmpty()){
return -1;
}
return elem[front];
}
2.4 Get tail elements
- Idea: If rear returns to the previous one at position 0, modulo arithmetic is required; it can be directly subtracted;
//获取队尾
public int Rear() {
//1.判断是否为空
if(isEmpty()){
return -1;
}
int index = this.rear==0 ? this.elem.length-1 : this.rear-1;
return elem[index];
}
2.5 Determine whether it is empty
- Idea: As long as rear == front is empty
//是否为空
public boolean isEmpty() {
if(rear == front){
return true;
}
return false;
}
2.6 Determine whether it is full
- Idea: Just judge whether the next rear is the head element;
public boolean isFull() {
if((rear+1)%elem.length == front){
return true;
}
return false;
}
3. Complete code
//循环队列（用数组实现）
class MyCircularQueue {
public int[] elem;
public int front;//队头
public int rear;//队尾
/** Initialize your data structure here. Set the size of the queue to be k. */
//构造方法
public MyCircularQueue(int k) {
this.elem = new int[k+1];
}
/** Insert an element into the circular queue. Return true if the operation is successful. */
//入队
public boolean enQueue(int value) {
//1.先判断是否为满
if(isFull()){
return false;
}
this.elem[rear] = value;
rear = (rear+1)%this.elem.length;
return true;
}
/** Delete an element from the circular queue. Return true if the operation is successful. */
//出队
public boolean deQueue() {
//1.判断是否为空
if(isEmpty()){
return false;
}
front = (front+1)%elem.length;
return true;
}
/** Get the front item from the queue. */
//获取队头元素
public int Front() {
//1.判断是否为空
if(isEmpty()){
return -1;
}
return elem[front];
}
/** Get the last item from the queue. */
//获取队尾
public int Rear() {
//1.判断是否为空
if(isEmpty()){
return -1;
}
int index = this.rear==0 ? this.elem.length-1 : this.rear-1;
return elem[index];
}
/** Checks whether the circular queue is empty or not. */
//是否为空
public boolean isEmpty() {
if(rear == front){
return true;
}
return false;
}
/** Checks whether the circular queue is full or not. */
//是否为满
public boolean isFull() {
if((rear+1)%elem.length == front){
return true;
}
return false;
}
}
public class TestDemo4 {
public static void main(String[] args) {
MyCircularQueue myCircularQueue = new MyCircularQueue(8);
myCircularQueue.enQueue(1);
myCircularQueue.enQueue(2);
myCircularQueue.enQueue(3);
myCircularQueue.enQueue(4);
System.out.println(myCircularQueue.Front());
System.out.println(myCircularQueue.Rear());
}
}