标签：des style blog color 使用 os io for
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：使用map和list实现LRU cache，map能够加速查找速度，而list能够快速地动态插入和删除节点。
每次若访问命中，即key存在于cache中，则将其对应的list中的元素移至list首部。然后，对于get，返回list首部元素的value值；对于set，修改list首部元素的value值。
若访问未命中，对于get，返回-1；对于set，将新的“key-地址”映射和“key-value”值对分别插入map中和list的首部。
若cache已达到容量上限，则插入新元素之后，应从list尾部删除一个元素，并将其key值对应的“key-地址”映射从map中删除。
1 class Node 2 { 3 public: 4 Node(): key(-1), value(-1) {} 5 Node( int aKey, int aValue ): key(aKey), value(aValue) {} 6 int key; 7 int value; 8 }; 9 10 class LRUCache{ 11 public: 12 LRUCache(int capacity) { this->capacity = capacity; } 13 14 int get(int key) { 15 if( cacheMap.find( key ) != cacheMap.end() ) { 16 list<Node>::iterator iter = cacheMap[key]; 17 cacheList.splice( cacheList.begin(), cacheList, iter ); 18 cacheMap[key] = cacheList.begin(); 19 return cacheList.begin()->value; 20 } 21 return -1; 22 } 23 24 void set(int key, int value) { 25 if( cacheMap.find( key ) != cacheMap.end() ) { 26 list<Node>::iterator iter = cacheMap[key]; 27 cacheList.splice( cacheList.begin(), cacheList, iter ); 28 cacheMap[key] = cacheList.begin(); 29 cacheList.begin()->value = value; 30 } else { 31 if( cacheMap.size() == capacity ) { 32 cacheMap.erase( cacheList.back().key ); 33 cacheList.pop_back(); 34 } 35 cacheList.push_front( Node(key,value) ); 36 cacheMap[key] = cacheList.begin(); 37 } 38 } 39 40 public: 41 int capacity; 42 list<Node> cacheList; 43 unordered_map<int,list<Node>::iterator> cacheMap; 44 };
标签：des style blog color 使用 os io for
原文地址：http://www.cnblogs.com/moderate-fish/p/3904029.html
