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

import "container/list"

type KeyValue struct {
	key int
	val int
}

type LRUCache struct {
	m        map[int]*list.Element
	q        *list.List
	capacity int
}

func Constructor(capacity int) LRUCache {
	return LRUCache{make(map[int]*list.Element), list.New(), capacity}
}

func (this *LRUCache) Get(key int) int {
	if n, ok := this.m[key]; ok {
		this.q.MoveToFront(n)
		return n.Value.(KeyValue).val
	}
	return -1
}

func (this *LRUCache) Put(key int, value int) {
	kv := KeyValue{key, value}

	if n, ok := this.m[key]; ok {
		n.Value = kv
		this.q.MoveToFront(n)
		this.m[key] = n
	} else {
		this.m[key] = this.q.PushFront(kv)
	}

	if len(this.m) > this.capacity {
		delete(this.m, this.q.Back().Value.(KeyValue).key)
		this.q.Remove(this.q.Back())
	}
}

/**
 * Your LRUCache object will be instantiated and called as such:
 * obj := Constructor(capacity);
 * param_1 := obj.Get(key);
 * obj.Put(key,value);
 */

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