标签：div invalid lis array 就是 cee 实现 while return
https://en.wikipedia.org/wiki/Circular_buffer
microsoft on site面试问到到一个，当时有点紧张，然后用链表实现，最后写的也有些问题，要求的单元测试也没有完成。
两种实现，使用数组或者链表，相对来说不需要随机访问，使用链表会更好，实现上链表也更容易些。
接口定义，实际使用应该定义泛型接口
package com.ljw.javatest; // Ringbuffer is a circle, and has a head and tail. // When add item, add item at tail, if item‘s quantity exceed max, // then delete the head item. public interface RingBuffer{ public void addItem(int value); //return the oldest item public Integer getItem(); //delege the oldest item public void deleteItem(); //return item from head to tail public Integer[] getAll(); }
链表实现，定义了一个内部类存储节点
package com.ljw.javatest; public class RingBufferWithLinked implements RingBuffer{ class Node{ Integer value; Node next; Node(Integer value){ this.value=value; } } private int max; private int count; private Node head; private Node tail; public RingBufferWithLinked(int max) throws Exception { if(max<=0){ throw new Exception("invalid max"); } this.max=max; this.count=0; } @Override public void addItem(int value) { if(head==null){ head=new Node(value); tail=head; count++; return; } Node temp = new Node(value); tail.next = temp; tail = temp; if (count < max) { count++; return; } head=head.next; } @Override public Integer getItem() { if(head!=null){ return head.value; } return null; } @Override public void deleteItem() { if(head==null){ return; } head=head.next; count--; if(count==0){ head=tail=null; } } @Override public Integer[] getAll() { if(head==null){ return null; } Integer[] result=new Integer[count]; int i=0; Node temp=head; while(temp!=null){ result[i++]=temp.value; temp=temp.next; } return result; } }
数组实现，如果说不好，可能就是需要分配连续空间，以及最大不能超过数组最大长度
package com.ljw.javatest; import java.util.List; public class RingBufferWithArray implements RingBuffer { public static void main(String[] args) { } Integer[] buffer; int head; int tail; int max; int count; public RingBufferWithArray(int max) throws Exception { if (max <= 0) { throw new Exception("invalid max"); } buffer = new Integer[max]; this.max = max; count = 0; head = -1; tail = -1; } @Override public void addItem(int value) { if (count + 1 > max) { buffer[head] = value; tail = head; if (head == max - 1) { head = 0; } else { head++; } } else { count++; if (count == 1) { head=tail=0; buffer[head]=value; } else { if (tail == max - 1) { tail = 0; buffer[tail] = value; } else { buffer[++tail] = value; } } } } @Override public Integer getItem() { if (head == -1) { return null; } else { return buffer[head]; } } @Override public void deleteItem() { if (count == 0) { return; } buffer[head] = null; count--; if (count == 0) { head = tail = -1; } if (head++ == max) { head = 0; } } @Override public Integer[] getAll() { if (head == -1) { return null; } Integer[] result = new Integer[count]; for (int i = 0, temp = head; i < count; i++, temp++) { if (temp == max) { temp = 0; } result[i] = buffer[temp]; } return result; } }
测试，主要的边界情况是max=1，以及增加元素超过时如何处理。
package com.ljw.javatest; public class App { public static void main(String[] args) throws Exception { int max=3;//max=1; RingBuffer rb=new RingBufferWithLinked(max); rb.addItem(1); print(rb.getItem()==1); rb.deleteItem(); print(rb.getItem()==null); int add=2; for(int i=0;i<max+add;i++){ rb.addItem(i); } Integer[] result=rb.getAll(); for(int i=0;i<max;i++){ print(result[i]==i+add); } } public static void print(Object value){ System.out.println(value); } }
标签：div invalid lis array 就是 cee 实现 while return
原文地址：https://www.cnblogs.com/lvjianwei/p/11161325.html
