最近最少使用算法有两种实现方式:
(1)记时法:对于每一页增设一个访问时间计时器。每当一个页面被访问时,当时的绝对时钟内容被复制到对应的访问时间计时器中。这样系统就记录了内存中所有页面最后一次被访问的时间。淘汰时,选取访问时间计时器值中最小者对应的页面。
import java.util.Date; // IMPORT LIBRARY PACKAGES NEEDED BY YOUR PROGRAM // SOME CLASSES WITHIN A PACKAGE MAY BE RESTRICTED // DEFINE ANY CLASS AND METHOD NEEDED // CLASS BEGINS, THIS CLASS IS REQUIRED public class LeastRecentPage { // METHOD SIGNATURE BEGINS, THIS METHOD IS REQUIRED public static void main(String[] args) { // TODO Auto-generated method stub int[] pages = {7,0,1,2,0,3,0,4,2,3,0,3,2,1,2,0};//结果是11; System.out.println(lruCountMiss(3, pages)); } public static int lruCountMiss(int max_cache_size, int[] pages) { // INSERT YOUR CODE HERE int[] cache = new int[max_cache_size]; int TIME = 1; int[] time=new int[max_cache_size]; int index=-1; int miss=0; L: for(int k=0;k<pages.length;k++){ int min = Integer.MAX_VALUE; int min_index=0; for(int i=0;i<max_cache_size;i++){ index = (index+1)%max_cache_size; if(time[index]==0){ cache[index]=pages[k]; time[index]= TIME++; miss++; continue L; } if(cache[index]==pages[k]){ time[index] = TIME++; continue L; } if(time[index]<min){ min = time[index]; min_index = index; } } miss++; cache[min_index]=pages[k]; time[min_index]= TIME++; index=min_index; } return miss; } // METHOD SIGNATURE ENDS }
(2)栈法:按照页面最后一次访问的时间次序将页面号依次排列到栈中。当一个页面最访问时,其对应的页面号由站内取出送入栈顶。淘汰时,取栈底页面号所对应的页面。这里的栈不是通常定义的先入先出栈。为了便于对栈中任意位置的操作,应用双向链表来构造栈。
import java.util.LinkedList; import java.util.List; // IMPORT LIBRARY PACKAGES NEEDED BY YOUR PROGRAM // SOME CLASSES WITHIN A PACKAGE MAY BE RESTRICTED // DEFINE ANY CLASS AND METHOD NEEDED // CLASS BEGINS, THIS CLASS IS REQUIRED public class LeastRecentPage { // METHOD SIGNATURE BEGINS, THIS METHOD IS REQUIRED public static void main(String[] args) { // TODO Auto-generated method stub int[] pages = {7,0,1,2,0,3,0,4,2,3,0,3,2,1,2,0};//结果是11; System.out.println(LinkedListlruCountMiss(3, pages)); } public static int LinkedListlruCountMiss(int max_cache_size, int[] pages) { // INSERT YOUR CODE HERE int[] cache = new int[max_cache_size]; List<Integer> li = new LinkedList<Integer>(); int index=-1; int miss=0; L: for(int k=0;k<pages.length;k++){ for(int i=0;i<max_cache_size;i++){ index = (index+1)%max_cache_size; if(cache[index]==pages[k]){ li.remove(new Integer(index)); li.add(new Integer(index)); continue L; } } miss++; if(cache[index]==0){ li.add(index); continue L; } index = li.remove(li.size()-1); li.add(new Integer(index)); cache[index] = pages[k]; } return miss; } // METHOD SIGNATURE ENDS }
运行结果都是:11次。
最近最少使用算法的实现开销是很大的。