LRU Cache.cpp

/*
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 /* capacity */ );

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:
    int cap;
    vector<pair<int,int> > v;
    public:
        LRUCache(int capacity) {
            cap = capacity;
        }

        int get(int key) {
            // cout<<"\nGETT->1";
            // for(int i=0;i<v.size();i++)
            // {
            //     int x=v[i].first;
            //     int y=v[i].second;
            //     cout<<"("<<x<<","<<y<<")";
            // }
            for(int i=0;i<v.size();i++)
            {
                if(v[i].first == key)
                {
                    int x=v[i].first;
                    int y=v[i].second;
                    v.erase(v.begin()+i);
                    v.push_back(make_pair(x,y));
                    // cout<<"\nGET-->2";
                    // for(int i=0;i<v.size();i++)
                    // {
                    //     int xx=v[i].first;
                    //     int yy=v[i].second;
                    //     cout<<"("<<xx<<","<<yy<<")";
                    // }
                    return y;
                }
            }
            return -1;
        }

        void put(int key, int value) {
            if(v.size()<cap)
            {
                for(int i=0;i<v.size();i++)
                {
                    if(v[i].first == key)
                    {
                        v.erase(v.begin()+i);
                    }
                }
                v.push_back(make_pair(key,value));
            }else
            {
                int flg=0;
                for(int i=0;i<v.size();i++)
                {
                    if(v[i].first == key)
                    {
                        v.erase(v.begin()+i);
                        flg = 1;
                    }
                }
                if(flg==0)
                    v.erase(v.begin());
                v.push_back(make_pair(key,value));
            }
            // cout<<"\n Put-->"<<endl;
            // for(int i=0;i<v.size();i++)
            // {
            //     int x=v[i].first;
            //     int y=v[i].second;
            //     cout<<"("<<x<<","<<y<<")";
            // }
        }
};

/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache* obj = new LRUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */