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day-24.cpp
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day-24.cpp
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/*
Question: Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.
get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
put(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.
The cache is initialized with a positive capacity.
Follow up:
Could you do both operations in O(1) time complexity?
Example:
LRUCache cache = new LRUCache(2)
cache.put(1, 1);
cache.put(2, 2);
cache.get(1); // returns 1
cache.put(3, 3); // evicts key 2
cache.get(2); // returns -1 (not found)
cache.put(4, 4); // evicts key 1
cache.get(1); // returns -1 (not found)
cache.get(3); // returns 3
cache.get(4); // returns 4
*/
class LRUCache {
public:
unordered_map<int, pair<int, list<int>::iterator>> hashMap;
int mCapacity;
list<int> keys;
LRUCache(int capacity) {
mCapacity = capacity;
}
int get(int key) {
if (hashMap.find(key) != hashMap.end()) {
keys.erase(hashMap[key].second);
keys.push_front(key);
hashMap[key].second = keys.begin();
return hashMap[key].first;
}
return -1;
}
void put(int key, int value) {
if (hashMap.find(key) != hashMap.end()) {
keys.erase(hashMap[key].second);
keys.push_front(key);
} else {
if (keys.size() == mCapacity) {
hashMap.erase(keys.back());
keys.pop_back();
}
keys.push_front(key);
}
hashMap[key] = make_pair(value, keys.begin());
}
};