[hard]146. LRU Cache

146. LRU Cache

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.

很简单，使用hash或者map维护数据和时间的关系

class LRUCache{
map <int, int> data;
map <int, int > timer;
map <int, int> data_time;

int cap, time;
public:
LRUCache(int capacity) {
cap = capacity;
time = 0;
}

void timer_check() {
while (0 == data_time.count(timer.begin() -> second) ||
data_time[timer.begin() -> second] != timer.begin() -> first)
timer.erase(timer.begin());
}

void check() {
timer_check();
while (data.size() > cap) {
data.erase(timer.begin() -> second);
data_time.erase(timer.begin() -> second);
timer.erase(timer.begin());
timer_check();
}
}

int get(int key) {
if (data.count(key)) {
++ time;
timer[time] = key;
data_time[key] = time;
timer_check();
return data[key];
}
return -1;
}