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253 lines (207 loc) · 5.98 KB
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// Source : https://oj.leetcode.com/problems/lru-cache/
// Author : Hao Chen
// Date : 2014-10-12
/**********************************************************************************
*
* 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.
*
**********************************************************************************/
#include <stdlib.h>
#include <time.h>
#include <iostream>
#include <map>
using namespace std;
// The idea here is quite simple:
// 1) A Map to index the key. O(1) key search time-complexity.
// 2) A List to sort the cache data by accessed time.
//
// Considering there are too many insert/delete opreations for the List,
// The ouble linked list is the good data structure to performance it.
class Node {
public:
int key;
int value;
Node *next, *prev;
Node(int k, int v) { key=k; value=v; next = prev = NULL; }
//Node(int k, int v, Node* n=NULL, Node* p=NULL): key(k), value(v), next(n), prev(p) {}
};
// the following double linked list seems a bit commplicated.
class DoubleLinkedList {
private:
Node *pHead, *pTail;
int size;
public:
DoubleLinkedList(){
pHead = pTail = NULL;
size = 0;
}
~DoubleLinkedList() {
while(pHead!=NULL){
Node*p = pHead;
pHead = pHead->next;
delete p;
}
}
int Size() const {
return size;
}
Node* NewAtBegin(int key, int value) {
Node *n = new Node(key, value);
return AddAtBegin(n);
}
Node* NewAtEnd(int key, int value) {
Node *n = new Node(key, value);
return AddAtEnd(n);
}
Node* AddAtBegin(Node* n){
size++;
if (pHead==NULL) {
pHead = pTail = n;
return n;
}
n->next = pHead;
n->prev = NULL;
pHead->prev = n;
pHead = n;
return n;
}
Node* AddAtEnd(Node* n) {
size++;
if (pHead==NULL) {
pHead = pTail = n;
return n;
}
pTail->next = n;
n->prev = pTail;
n->next = NULL;
pTail = n;
}
void Unlink(Node* n){
Node* before = n->prev;
Node* after = n->next;
if (before){
before->next = after;
}
if (after){
after->prev = before;
}
if(pHead == n){
pHead = pHead->next;
}else if(pTail == n) {
pTail = pTail->prev;
}
size--;
}
void Delete(Node* n){
Unlink(n);
delete n;
}
void TakeToBegin(Node* n){
Unlink(n);
AddAtBegin(n);
}
Node* GetTailNode() {
return pTail;
}
void DeleteLast() {
Delete(pTail);
}
void Print(){
Node* p = pHead;
while(p!=NULL) {
cout << "(" << p->key << "," << p->value << ") ";
p = p->next;
}
cout << endl;
}
};
class LRUCache{
private:
//cacheList - store the date
DoubleLinkedList cacheList;
//cacheMap - index the date for searching
map<int, Node*> cacheMap;
//the max capcity of cache
int capacity;
public:
LRUCache(int capacity) {
this->capacity = capacity;
}
void print(){
cacheList.Print();
}
int get(int key) {
// The accessed node must be up-to-time -- take to the front
if (cacheMap.find(key) != cacheMap.end() ){
cacheList.TakeToBegin(cacheMap[key]);
return cacheMap[key]->value;
}
return -1;
}
void set(int key, int value) {
// key found, update the data, and take to the front
if (cacheMap.find(key) != cacheMap.end() ){
Node *p = cacheMap[key];
p->value = value;
cacheList.TakeToBegin(cacheMap[key]);
}else{
// key not found, new a node to store data
cacheMap[key] = cacheList.NewAtBegin(key, value);
// if the capacity exceed, remove the last one.
if( cacheList.Size() > capacity) {
int key = cacheList.GetTailNode()->key;
cacheMap.erase(key);
cacheList.DeleteLast();
}
}
}
};
int main(int argc, char** argv)
{
/*
LRUCache c(2);
c.set(2,1);
c.print();
c.set(2,2);
c.print();
c.get(2);
c.print();
c.set(1,1);
c.print();
c.set(4,1);
c.print();
c.get(2);
c.print();
cout << "---------" << endl;
*/
srand(time(0));
int capacity = 5;
int test_loop_times = 10;
if (argc>1){
capacity = atoi(argv[1]);
}
if (argc>2){
test_loop_times = atoi(argv[1]);
}
LRUCache cache(capacity);
int v;
for(int i=0; i<test_loop_times; i++) {
v = i;//rand() % capacity;
cout << "set " << v << ": ";
cache.set(v, v);
cache.print();
v = rand() % capacity;
cout << "get " << v << ": " << cache.get(v);
cache.print();
cout << endl;
}
return 0;
}