LeetCode 146 LRU Cache (C++, Python)

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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.
Solution (C++)


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class LRUCache{
private:
    unordered_map<int, pair<int, list<int>::iterator>> cache;
    int room;
    list<int> accessOrder;
public:
    LRUCache(int capacity):room(capacity) {


    }

    int get(int key) {
        auto it = cache.find(key);
        if (it == cache.end()) return -1;
        int ret = it->second.first;
        if (it->second.second != next(accessOrder.end(), - 1)) {
            accessOrder.splice(accessOrder.end(), accessOrder, it->second.second);
        }
        return ret;
    }

    void set(int key, int value) {
        auto it = cache.find(key);
        if (it == cache.end()) {
            if (room == 0) {
                auto it = cache[accessOrder.front()].second;
                cache.erase(accessOrder.front());
                accessOrder.erase(it);
            } else {
                -- room;
            }
            accessOrder.push_back(key);
            cache.insert({key, {value, next(accessOrder.end(), -1)}});
        } else {
            it->second.first = value;
            if (it->second.second != next(accessOrder.end(), - 1)) {
                accessOrder.splice(accessOrder.end(), accessOrder, it->second.second);
            }
        }
    }
};
Solution (Python)


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from collections import OrderedDict
class LRUCache:

    # @param capacity, an integer
    def __init__(self, capacity):
        self.room = capacity
        self.ordmap = OrderedDict()

    # @return an integer
    def get(self, key):
        if key in self.ordmap:
            ret = self.ordmap[key]
            del self.ordmap[key]
            self.ordmap[key] = ret
            return ret
        else:
            return -1
        

    # @param key, an integer
    # @param value, an integer
    # @return nothing
    def set(self, key, value):
        if key in self.ordmap:
            del self.ordmap[key]
            self.ordmap[key] = value
        else:
            if self.room:
                self.ordmap[key] = value
                self.room -= 1
            else:
                self.ordmap.popitem(last=False)
                self.ordmap[key] = value

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