Merge pull request wangzheng0822#184 from SpecialYy/master

lruBasedArray

Author: wangzheng0822

java/06_linkedlist/LRUBasedArray.java

@@ -0,0 +1,173 @@
+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) {
+ value[--count] = null;
+ 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);
+ }
+ }
+}