Adding readme file

Author: bugsweeper

146-LRUCache/README.md

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+Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.
+
+Implement the LRUCache class:
+
+
+	LRUCache(int capacity) Initialize the LRU cache with positive size capacity.
+	int get(int key) Return the value of the key if the key exists, otherwise return -1.
+	void put(int key, int value) Update the value of the key if the key exists. Otherwise, add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation, evict the least recently used key.
+
+
+The functions get and put must each run in O(1) average time complexity.
+
+ 
+Example 1:
+
+Input
+["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"]
+[[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]
+Output
+[null, null, null, 1, null, -1, null, -1, 3, 4]
+
+Explanation
+LRUCache lRUCache = new LRUCache(2);
+lRUCache.put(1, 1); // cache is {1=1}
+lRUCache.put(2, 2); // cache is {1=1, 2=2}
+lRUCache.get(1);    // return 1
+lRUCache.put(3, 3); // LRU key was 2, evicts key 2, cache is {1=1, 3=3}
+lRUCache.get(2);    // returns -1 (not found)
+lRUCache.put(4, 4); // LRU key was 1, evicts key 1, cache is {4=4, 3=3}
+lRUCache.get(1);    // return -1 (not found)
+lRUCache.get(3);    // return 3
+lRUCache.get(4);    // return 4
+
+
+ 
+Constraints:
+
+
+	1 <= capacity <= 3000
+	0 <= key <= 104
+	0 <= value <= 105
+	At most 2 * 105 calls will be made to get and put.
+