LRU Cache

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.

 

思路：用HashMap和双向链表来实现

参考：http://www.programcreek.com/2013/03/leetcode-lru-cache-java/

java代码：

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