Problem LRU Cache

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Problem Description:

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

 

 Solution:

 1     public static class DoubleLinkedListNode { 2         int val; 3         int key; 4         DoubleLinkedListNode pre; 5         DoubleLinkedListNode next; 6         DoubleLinkedListNode(int key, int val) {this.key = key; this.val = val;pre = null; next = null;} 7     } 8     private int capacity; 9 10     private int len;11     private HashMap<Integer, DoubleLinkedListNode> map = 12                                 new HashMap<Integer, DoubleLinkedListNode>();13     private DoubleLinkedListNode head;14     private DoubleLinkedListNode end;15     public LRUCache(int capacity) {16         this.capacity = capacity;17 18         len = 0;19     }20 21     public int get(int key) {22     23         if (map.containsKey(key)) {24             DoubleLinkedListNode latest = map.get(key);25             removeNode(latest);26             setHead(latest);27             return latest.val;28         } else {29             return -1;30         }31 32     }33     public void removeNode(DoubleLinkedListNode node) {34         DoubleLinkedListNode cur = node;35         DoubleLinkedListNode pre = cur.pre;36         DoubleLinkedListNode post = cur.next;37 38         if (pre != null) {39             pre.next = post;40         } else {41             head = post;42         }43 44         if (post != null) {45             post.pre = pre;46         } else {47             end = pre;48         }49     }50     public void setHead(DoubleLinkedListNode node) {51         node.next = head;52         node.pre = null;53         if (head != null) {54             head.pre = node;55         }56 57         head = node;58         if (end == null) {59             end = node;60         }61     }62     public void set(int key, int value) {63 64         if (map.containsKey(key)) {65             DoubleLinkedListNode oldNode = map.get(key);66             oldNode.val = value;67             removeNode(oldNode);68             setHead(oldNode);69         } else {70             DoubleLinkedListNode newNode = new DoubleLinkedListNode(key, value);71             if (len < capacity) {72                 setHead(newNode);73                 map.put(key, newNode);74                 len++;75             } else {76                 map.remove(end.key);77                 end = end.pre;78                 if (end != null) {79                     end.next = null;80                 }81 82                 setHead(newNode);83                 map.put(key, newNode);84             }85         }86     87     }