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LRUCache.java
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LRUCache.java
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package design;
// Source : https://leetcode.com/problems/lru-cache/
// Id : 146
// Author : Fanlu Hai | https://github.com/Fanlu91/FanluLeetcode
// Date : 2019-06-13
// Topic : Design
// Level : Medium
// Other :
// Tips : Use double sentinel if there is a tail also.
// Result : 91.27% 67.29%
import java.util.HashMap;
public class LRUCache {
class Node {
int key;
int value;
Node next;
Node pre;
public Node() {
}
public Node(int key, int value) {
this.key = key;
this.value = value;
}
}
int size, maxSize;
HashMap<Integer, Node> map;
/*
Node sentinel, tail;
// 31.87% 67 ms 69.05%
public LRUCache(int capacity) {
this.size = 0;
this.maxSize = capacity;
this.map = new HashMap<>();
this.sentinel = new Node(-1, -1);
}
public int getOrigin(int key) {
Node tmpNode;
if (map.containsKey(key)) {
tmpNode = map.get(key);
if (tail != tmpNode) {
tmpNode.pre.next = tmpNode.next;
tmpNode.next.pre = tmpNode.pre;
tail.next = tmpNode;
tmpNode.pre = tail;
tail = tmpNode;
}
return tmpNode.value;
} else
return -1;
}
public void putOrigin(int key, int value) {
Node newNode = new Node(key, value);
Node tmpNode;
if (size == 0) {
newNode.pre = sentinel;
sentinel.next = newNode;
tail = newNode;
map.put(key, newNode);
size = 1;
} else if (size == maxSize) {
if (map.containsKey(key)) {
tmpNode = map.get(key);
if (tail != tmpNode) {
tmpNode.pre.next = tmpNode.next;
tmpNode.next.pre = tmpNode.pre;
tail.next = newNode;
newNode.pre = tail;
tail = newNode;
} else {
tail.pre.next = newNode;
newNode.pre = tail.pre;
tail = newNode;
}
} else {
tmpNode = sentinel.next;
if (tmpNode != tail) {
sentinel.next = tmpNode.next;
tmpNode.next.pre = sentinel;
tail.next = newNode;
newNode.pre = tail;
tail = newNode;
} else {
sentinel.next = newNode;
newNode.pre = sentinel;
tail = newNode;
}
map.remove(tmpNode.key);
}
map.put(key, newNode);
} else {
if (map.containsKey(key)) {
tmpNode = map.get(key);
if (tmpNode != tail) {
tmpNode.pre.next = tmpNode.next;
tmpNode.next.pre = tmpNode.pre;
tail.next = newNode;
newNode.pre = tail;
} else {
newNode.pre = tail.pre;
tail.pre.next = newNode;
}
} else {
tail.next = newNode;
newNode.pre = tail;
size++;
}
tail = newNode;
map.put(key, newNode);
}
}*/
// my original approach store the last visit at tail below used the opposite
// it also used double sentinel, which is the main difference
Node sentinelHead, sentinelTail;
// 91.27% 59 ms 67.29%
public LRUCache(int capacity) {
this.size = 0;
this.maxSize = capacity;
this.map = new HashMap<>();
sentinelHead = new Node();
sentinelTail = new Node();
sentinelHead.next = sentinelTail;
sentinelTail.pre = sentinelHead;
}
public void addNode(Node node) {
node.pre = sentinelHead;
node.next = sentinelHead.next;
sentinelHead.next.pre = node;
sentinelHead.next = node;
}
public void removeNode(Node node) {
node.pre.next = node.next;
node.next.pre = node.pre;
}
public void moveToHead(Node node) {
removeNode(node);
addNode(node);
}
public Node popTail() {
Node res = sentinelTail.pre;
removeNode(res);
return res;
}
public int get(int key) {
Node tmp = map.get(key);
if (tmp == null)
return -1;
else {
moveToHead(tmp);
}
return tmp.value;
}
public void put(int key, int value) {
Node node = map.get(key);
if (node == null) {
Node newNode = new Node(key, value);
map.put(key, newNode);
addNode(newNode);
size++;
if (size > maxSize) {
Node tail = popTail();
map.remove(tail.key);
--size;
}
} else {
node.value = value;
moveToHead(node);
}
}
public static void main(String[] args) {
/* LRUCache l = new LRUCache(1);
l.put(2, 1);
l.get(2);
l.put(3,2);
l.get(2);
l.get(3);*/
LRUCache l = new LRUCache(2);
l.put(2, 1);
l.put(2, 2);
l.get(2);
l.put(1, 1);
l.put(4, 1);
l.get(2);
}
}
/**
* 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);
*/