# problem0146

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Published: Jul 25, 2019 License: MIT

### 146. LRU Cache

#### 题目

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.

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.put(4, 4);    // evicts key 1
cache.get(3);       // returns 3
cache.get(4);       // returns 4
``````

#### 解题思路

LRU缓存利用了这样的一种思想。LRU是Least Recently Used 的缩写，翻译过来就是“最近最少使用”，也就是说，LRU缓存把最近最少使用的数据移除，让给最新读取的数据。而往往最常读取的，也是读取次数最多的，所以，利用LRU缓存，我们能够提高系统的performance.

## Documentation ¶

### Constants ¶

This section is empty.

### Variables ¶

This section is empty.

### Functions ¶

This section is empty.

### Types ¶

#### type LRUCache ¶

```type LRUCache struct {
// contains filtered or unexported fields
}```

LRUCache contains a hash map and a doubly linked list

#### func Constructor ¶

`func Constructor(capacity int) LRUCache`

Constructor initializes a new LRUCache.

#### func (*LRUCache) Get ¶

`func (c *LRUCache) Get(key int) int`

Get a list node from the hash map.

#### func (*LRUCache) Put ¶

`func (c *LRUCache) Put(key int, value int)`

Put key and value in the LRUCache

#### type Pair ¶

```type Pair struct {
// contains filtered or unexported fields
}```

Pair is the value of a list node.