/**
Design a data structure that follows the constraints of a Least Recently Used (
LRU) cache.
Implement the LRUCache class:
LRUCache(int capacity) Initialize the LRU cache with positive size capacity.
int get(int key) Return the value of the key if the key exists, otherwise
return -1.
void put(int key, int value) Update the value of the key if the key exists.
Otherwise, add the key-value pair to the cache. If the number of keys exceeds the
capacity from this operation, evict the least recently used key.
The functions get and put must each run in O(1) average time complexity.
Example 1:
Input
["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"]
[[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]
Output
[null, null, null, 1, null, -1, null, -1, 3, 4]
Explanation
LRUCache lRUCache = new LRUCache(2);
lRUCache.put(1, 1); // cache is {1=1}
lRUCache.put(2, 2); // cache is {1=1, 2=2}
lRUCache.get(1); // return 1
lRUCache.put(3, 3); // LRU key was 2, evicts key 2, cache is {1=1, 3=3}
lRUCache.get(2); // returns -1 (not found)
lRUCache.put(4, 4); // LRU key was 1, evicts key 1, cache is {4=4, 3=3}
lRUCache.get(1); // return -1 (not found)
lRUCache.get(3); // return 3
lRUCache.get(4); // return 4
Constraints:
1 <= capacity <= 3000
0 <= key <= 10⁴
0 <= value <= 10⁵
At most 2 * 10⁵ calls will be made to get and put.
Related Topics设计 | 哈希表 | 链表 | 双向链表
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*/
//leetcode submit region begin(Prohibit modification and deletion)
class LRUCache {
class LruNode {
int key;
int value;
LruNode left;
LruNode right;
}
private Map<Integer, LruNode> lruMap = new HashMap<>();
private LruNode head, tail;
private int capacity;
public LRUCache(int capacity) {
this.lruMap = new HashMap<>(capacity);
this.capacity = capacity;
}
public int get(int key) {
LruNode node = lruMap.get(key);
if (node == null) {
return -1;
}
LruNode leftNode = node.left;
LruNode rightNode = node.right;
if (tail == node) {
return node.value;
}
if (leftNode != null) {
leftNode.right = rightNode;
rightNode.left = leftNode;
} else if (rightNode != null) {
rightNode.left = null;
head = rightNode;
}
tail.right = node;
node.left = tail;
node.right = null;
tail = node;
return node.value;
}
public void put(int key, int value) {
if (lruMap.containsKey(key)) {
LruNode node = lruMap.get(key);
node.value = value;
get(key);
return;
}
if (lruMap.size() == this.capacity) {
LruNode head = this.head;
lruMap.remove(head.key);
if (head.right != null) {
head.right.left = null;
}
this.head = head.right;
}
LruNode newNode = new LruNode();
newNode.key = key;
newNode.value = value;
if (head == null) {
head = newNode;
newNode.left = null;
} else {
newNode.left = tail;
tail.right = newNode;
}
newNode.right = null;
tail = newNode;
lruMap.put(key, newNode);
}
}
/**
* Your LRUCache object will be instantiated and called as such:
* LRUCache obj = new LRUCache(capacity);
* int param_1 = obj.get(key);
* obj.put(key,value);
*/
//leetcode submit region end(Prohibit modification and deletion)
