175 lines
4.3 KiB
Java
175 lines
4.3 KiB
Java
package linkedlist;
|
|
|
|
import java.util.HashMap;
|
|
import java.util.Map;
|
|
/**
|
|
* Created by SpecialYang in 2018/12/7 2:00 PM.
|
|
*
|
|
* 基于数组实现的LRU缓存
|
|
* 1. 空间复杂度为O(n)
|
|
* 2. 时间复杂度为O(n)
|
|
* 3. 不支持null的缓存
|
|
*/
|
|
public class LRUBasedArray<T> {
|
|
|
|
private static final int DEFAULT_CAPACITY = (1 << 3);
|
|
|
|
private int capacity;
|
|
|
|
private int count;
|
|
|
|
private T[] value;
|
|
|
|
private Map<T, Integer> holder;
|
|
|
|
public LRUBasedArray() {
|
|
this(DEFAULT_CAPACITY);
|
|
}
|
|
|
|
public LRUBasedArray(int capacity) {
|
|
this.capacity = capacity;
|
|
value = (T[]) new Object[capacity];
|
|
count = 0;
|
|
holder = new HashMap<T, Integer>(capacity);
|
|
}
|
|
|
|
/**
|
|
* 模拟访问某个值
|
|
* @param object
|
|
*/
|
|
public void offer(T object) {
|
|
if (object == null) {
|
|
throw new IllegalArgumentException("该缓存容器不支持null!");
|
|
}
|
|
Integer index = holder.get(object);
|
|
if (index == null) {
|
|
if (isFull()) {
|
|
removeAndCache(object);
|
|
} else {
|
|
cache(object, count);
|
|
}
|
|
} else {
|
|
update(index);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* 若缓存中有指定的值，则更新位置
|
|
* @param end
|
|
*/
|
|
public void update(int end) {
|
|
T target = value[end];
|
|
rightShift(end);
|
|
value[0] = target;
|
|
holder.put(target, 0);
|
|
}
|
|
|
|
/**
|
|
* 缓存数据到头部，但要先右移
|
|
* @param object
|
|
* @param end 数组右移的边界
|
|
*/
|
|
public void cache(T object, int end) {
|
|
rightShift(end);
|
|
value[0] = object;
|
|
holder.put(object, 0);
|
|
count++;
|
|
}
|
|
|
|
/**
|
|
* 缓存满的情况，踢出后，再缓存到数组头部
|
|
* @param object
|
|
*/
|
|
public void removeAndCache(T object) {
|
|
T key = value[--count];
|
|
holder.remove(key);
|
|
cache(object, count);
|
|
}
|
|
|
|
/**
|
|
* end左边的数据统一右移一位
|
|
* @param end
|
|
*/
|
|
private void rightShift(int end) {
|
|
for (int i = end - 1; i >= 0; i--) {
|
|
value[i + 1] = value[i];
|
|
holder.put(value[i], i + 1);
|
|
}
|
|
}
|
|
|
|
public boolean isContain(T object) {
|
|
return holder.containsKey(object);
|
|
}
|
|
|
|
public boolean isEmpty() {
|
|
return count == 0;
|
|
}
|
|
|
|
public boolean isFull() {
|
|
return count == capacity;
|
|
}
|
|
|
|
@Override
|
|
public String toString() {
|
|
StringBuilder sb = new StringBuilder();
|
|
for (int i = 0; i < count; i++) {
|
|
sb.append(value[i]);
|
|
sb.append(" ");
|
|
}
|
|
return sb.toString();
|
|
}
|
|
|
|
static class TestLRUBasedArray {
|
|
|
|
public static void main(String[] args) {
|
|
testDefaultConstructor();
|
|
testSpecifiedConstructor(4);
|
|
// testWithException();
|
|
}
|
|
|
|
private static void testWithException() {
|
|
LRUBasedArray<Integer> lru = new LRUBasedArray<Integer>();
|
|
lru.offer(null);
|
|
}
|
|
|
|
public static void testDefaultConstructor() {
|
|
System.out.println("======无参测试========");
|
|
LRUBasedArray<Integer> lru = new LRUBasedArray<Integer>();
|
|
lru.offer(1);
|
|
lru.offer(2);
|
|
lru.offer(3);
|
|
lru.offer(4);
|
|
lru.offer(5);
|
|
System.out.println(lru);
|
|
lru.offer(6);
|
|
lru.offer(7);
|
|
lru.offer(8);
|
|
lru.offer(9);
|
|
System.out.println(lru);
|
|
}
|
|
|
|
public static void testSpecifiedConstructor(int capacity) {
|
|
System.out.println("======有参测试========");
|
|
LRUBasedArray<Integer> lru = new LRUBasedArray<Integer>(capacity);
|
|
lru.offer(1);
|
|
System.out.println(lru);
|
|
lru.offer(2);
|
|
System.out.println(lru);
|
|
lru.offer(3);
|
|
System.out.println(lru);
|
|
lru.offer(4);
|
|
System.out.println(lru);
|
|
lru.offer(2);
|
|
System.out.println(lru);
|
|
lru.offer(4);
|
|
System.out.println(lru);
|
|
lru.offer(7);
|
|
System.out.println(lru);
|
|
lru.offer(1);
|
|
System.out.println(lru);
|
|
lru.offer(2);
|
|
System.out.println(lru);
|
|
}
|
|
}
|
|
}
|