LeetCode-in-All

146. LRU Cache

Medium

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.

Solution

class LruCacheNode {
    public $key;
    public $value;
    public $prev;
    public $next;

    function __construct($k, $v) {
        $this->key = $k;
        $this->value = $v;
    }
}

class LRUCache {
    private $capacity;
    private $cacheMap;
    private $head;
    private $tail;

    /**
     * @param Integer $capacity
     */
    function __construct($cap) {
        $this->capacity = $cap;
        $this->cacheMap = array();
    }

    /**
     * @param Integer $key
     * @return Integer
     */
    public function get($key) {
        if (!isset($this->cacheMap[$key])) {
            return -1;
        }
        $val = $this->cacheMap[$key];
        $this->moveToHead($val);
        return $val->value;
    }

    /**
     * @param Integer $key
     * @param Integer $value
     * @return NULL
     */
    public function put($key, $value) {
        if (isset($this->cacheMap[$key])) {
            $valNode = $this->cacheMap[$key];
            $valNode->value = $value;
            $this->moveToHead($valNode);
        } else {
            if (count($this->cacheMap) < $this->capacity) {
                if (count($this->cacheMap) == 0) {
                    $node = new LruCacheNode($key, $value);
                    $this->cacheMap[$key] = $node;
                    $this->head = $node;
                    $this->tail = $node;
                } else {
                    $node = new LruCacheNode($key, $value);
                    $this->cacheMap[$key] = $node;
                    $node->next = $this->head;
                    $this->head->prev = $node;
                    $this->head = $node;
                }
            } else {
                $last = $this->tail;
                $this->tail = $last->prev;
                if ($this->tail != null) {
                    $this->tail->next = null;
                }
                unset($this->cacheMap[$last->key]);
                if (count($this->cacheMap) == 0) {
                    $this->head = null;
                }
                $this->put($key, $value);
            }
        }
    }

    private function moveToHead($node) {
        if ($node === $this->head) {
            return;
        }
        if ($node === $this->tail) {
            $this->tail = $node->prev;
        }
        $prev = $node->prev;
        $next = $node->next;
        $prev->next = $next;
        if ($next != null) {
            $next->prev = $prev;
        }
        $node->prev = null;
        $node->next = $this->head;
        $this->head->prev = $node;
        $this->head = $node;
    }
}
/**
 * Your LRUCache object will be instantiated and called as such:
 * $obj = LRUCache($capacity);
 * $ret_1 = $obj->get($key);
 * $obj->put($key, $value);
 */

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