LFU Cache
<p>Design and implement a data structure for a <a href="https://en.wikipedia.org/wiki/Least_frequently_used" target="_blank">Least Frequently Used (LFU)</a> cache.</p>

<p>Implement the <code>LFUCache</code> class:</p>

<ul>
	<li><code>LFUCache(int capacity)</code> Initializes the object with the <code>capacity</code> of the data structure.</li>
	<li><code>int get(int key)</code> Gets the value of the <code>key</code> if the <code>key</code> exists in the cache. Otherwise, returns <code>-1</code>.</li>
	<li><code>void put(int key, int value)</code> Update the value of the <code>key</code> if present, or inserts the <code>key</code> if not already present. When the cache reaches its <code>capacity</code>, it should invalidate and remove the <strong>least frequently used</strong> key before inserting a new item. For this problem, when there is a <strong>tie</strong> (i.e., two or more keys with the same frequency), the <strong>least recently used</strong> <code>key</code> would be invalidated.</li>
</ul>

<p>To determine the least frequently used key, a <strong>use counter</strong> is maintained for each key in the cache. The key with the smallest <strong>use counter</strong> is the least frequently used key.</p>

<p>When a key is first inserted into the cache, its <strong>use counter</strong> is set to <code>1</code> (due to the <code>put</code> operation). The <strong>use counter</strong> for a key in the cache is incremented either a <code>get</code> or <code>put</code> operation is called on it.</p>

<p>The functions&nbsp;<code data-stringify-type="code">get</code>&nbsp;and&nbsp;<code data-stringify-type="code">put</code>&nbsp;must each run in <code>O(1)</code> average time complexity.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input</strong>
[&quot;LFUCache&quot;, &quot;put&quot;, &quot;put&quot;, &quot;get&quot;, &quot;put&quot;, &quot;get&quot;, &quot;get&quot;, &quot;put&quot;, &quot;get&quot;, &quot;get&quot;, &quot;get&quot;]
[[2], [1, 1], [2, 2], [1], [3, 3], [2], [3], [4, 4], [1], [3], [4]]
<strong>Output</strong>
[null, null, null, 1, null, -1, 3, null, -1, 3, 4]

<strong>Explanation</strong>
// cnt(x) = the use counter for key x
// cache=[] will show the last used order for tiebreakers (leftmost element is  most recent)
LFUCache lfu = new LFUCache(2);
lfu.put(1, 1);   // cache=[1,_], cnt(1)=1
lfu.put(2, 2);   // cache=[2,1], cnt(2)=1, cnt(1)=1
lfu.get(1);      // return 1
                 // cache=[1,2], cnt(2)=1, cnt(1)=2
lfu.put(3, 3);   // 2 is the LFU key because cnt(2)=1 is the smallest, invalidate 2.
&nbsp;                // cache=[3,1], cnt(3)=1, cnt(1)=2
lfu.get(2);      // return -1 (not found)
lfu.get(3);      // return 3
                 // cache=[3,1], cnt(3)=2, cnt(1)=2
lfu.put(4, 4);   // Both 1 and 3 have the same cnt, but 1 is LRU, invalidate 1.
                 // cache=[4,3], cnt(4)=1, cnt(3)=2
lfu.get(1);      // return -1 (not found)
lfu.get(3);      // return 3
                 // cache=[3,4], cnt(4)=1, cnt(3)=3
lfu.get(4);      // return 4
                 // cache=[4,3], cnt(4)=2, cnt(3)=3
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= capacity&nbsp;&lt;= 10<sup>4</sup></code></li>
	<li><code>0 &lt;= key &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= value &lt;= 10<sup>9</sup></code></li>
	<li>At most <code>2 * 10<sup>5</sup></code>&nbsp;calls will be made to <code>get</code> and <code>put</code>.</li>
</ul>

<p>&nbsp;</p>
<span style="display: none;">&nbsp;</span>
['lru-cache', 'design-in-memory-file-system']
[]
[{"value": "cpp", "text": "C++", "defaultCode": "class LFUCache {\npublic:\n    LFUCache(int capacity) {\n        \n    }\n    \n    int get(int key) {\n        \n    }\n    \n    void put(int key, int value) {\n        \n    }\n};\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * LFUCache* obj = new LFUCache(capacity);\n * int param_1 = obj->get(key);\n * obj->put(key,value);\n */"}, {"value": "java", "text": "Java", "defaultCode": "class LFUCache {\n\n    public LFUCache(int capacity) {\n        \n    }\n    \n    public int get(int key) {\n        \n    }\n    \n    public void put(int key, int value) {\n        \n    }\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * LFUCache obj = new LFUCache(capacity);\n * int param_1 = obj.get(key);\n * obj.put(key,value);\n */"}, {"value": "python", "text": "Python", "defaultCode": "class LFUCache(object):\n\n    def __init__(self, capacity):\n        \"\"\"\n        :type capacity: int\n        \"\"\"\n        \n\n    def get(self, key):\n        \"\"\"\n        :type key: int\n        :rtype: int\n        \"\"\"\n        \n\n    def put(self, key, value):\n        \"\"\"\n        :type key: int\n        :type value: int\n        :rtype: None\n        \"\"\"\n        \n\n\n# Your LFUCache object will be instantiated and called as such:\n# obj = LFUCache(capacity)\n# param_1 = obj.get(key)\n# obj.put(key,value)"}, {"value": "python3", "text": "Python3", "defaultCode": "class LFUCache:\n\n    def __init__(self, capacity: int):\n        \n\n    def get(self, key: int) -> int:\n        \n\n    def put(self, key: int, value: int) -> None:\n        \n\n\n# Your LFUCache object will be instantiated and called as such:\n# obj = LFUCache(capacity)\n# param_1 = obj.get(key)\n# obj.put(key,value)"}, {"value": "c", "text": "C", "defaultCode": "\n\n\ntypedef struct {\n    \n} LFUCache;\n\n\nLFUCache* lFUCacheCreate(int capacity) {\n    \n}\n\nint lFUCacheGet(LFUCache* obj, int key) {\n    \n}\n\nvoid lFUCachePut(LFUCache* obj, int key, int value) {\n    \n}\n\nvoid lFUCacheFree(LFUCache* obj) {\n    \n}\n\n/**\n * Your LFUCache struct will be instantiated and called as such:\n * LFUCache* obj = lFUCacheCreate(capacity);\n * int param_1 = lFUCacheGet(obj, key);\n \n * lFUCachePut(obj, key, value);\n \n * lFUCacheFree(obj);\n*/"}, {"value": "csharp", "text": "C#", "defaultCode": "public class LFUCache {\n\n    public LFUCache(int capacity) {\n        \n    }\n    \n    public int Get(int key) {\n        \n    }\n    \n    public void Put(int key, int value) {\n        \n    }\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * LFUCache obj = new LFUCache(capacity);\n * int param_1 = obj.Get(key);\n * obj.Put(key,value);\n */"}, {"value": "javascript", "text": "JavaScript", "defaultCode": "/**\n * @param {number} capacity\n */\nvar LFUCache = function(capacity) {\n    \n};\n\n/** \n * @param {number} key\n * @return {number}\n */\nLFUCache.prototype.get = function(key) {\n    \n};\n\n/** \n * @param {number} key \n * @param {number} value\n * @return {void}\n */\nLFUCache.prototype.put = function(key, value) {\n    \n};\n\n/** \n * Your LFUCache object will be instantiated and called as such:\n * var obj = new LFUCache(capacity)\n * var param_1 = obj.get(key)\n * obj.put(key,value)\n */"}, {"value": "typescript", "text": "TypeScript", "defaultCode": "class LFUCache {\n    constructor(capacity: number) {\n        \n    }\n\n    get(key: number): number {\n        \n    }\n\n    put(key: number, value: number): void {\n        \n    }\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * var obj = new LFUCache(capacity)\n * var param_1 = obj.get(key)\n * obj.put(key,value)\n */"}, {"value": "php", "text": "PHP", "defaultCode": "class LFUCache {\n    /**\n     * @param Integer $capacity\n     */\n    function __construct($capacity) {\n        \n    }\n  \n    /**\n     * @param Integer $key\n     * @return Integer\n     */\n    function get($key) {\n        \n    }\n  \n    /**\n     * @param Integer $key\n     * @param Integer $value\n     * @return NULL\n     */\n    function put($key, $value) {\n        \n    }\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * $obj = LFUCache($capacity);\n * $ret_1 = $obj->get($key);\n * $obj->put($key, $value);\n */"}, {"value": "swift", "text": "Swift", "defaultCode": "\nclass LFUCache {\n\n    init(_ capacity: Int) {\n        \n    }\n    \n    func get(_ key: Int) -> Int {\n        \n    }\n    \n    func put(_ key: Int, _ value: Int) {\n        \n    }\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * let obj = LFUCache(capacity)\n * let ret_1: Int = obj.get(key)\n * obj.put(key, value)\n */"}, {"value": "kotlin", "text": "Kotlin", "defaultCode": "class LFUCache(capacity: Int) {\n\n    fun get(key: Int): Int {\n        \n    }\n\n    fun put(key: Int, value: Int) {\n        \n    }\n\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * var obj = LFUCache(capacity)\n * var param_1 = obj.get(key)\n * obj.put(key,value)\n */"}, {"value": "dart", "text": "Dart", "defaultCode": "class LFUCache {\n\n  LFUCache(int capacity) {\n    \n  }\n  \n  int get(int key) {\n    \n  }\n  \n  void put(int key, int value) {\n    \n  }\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * LFUCache obj = LFUCache(capacity);\n * int param1 = obj.get(key);\n * obj.put(key,value);\n */"}, {"value": "golang", "text": "Go", "defaultCode": "type LFUCache struct {\n    \n}\n\n\nfunc Constructor(capacity int) LFUCache {\n    \n}\n\n\nfunc (this *LFUCache) Get(key int) int {\n    \n}\n\n\nfunc (this *LFUCache) Put(key int, value int)  {\n    \n}\n\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * obj := Constructor(capacity);\n * param_1 := obj.Get(key);\n * obj.Put(key,value);\n */"}, {"value": "ruby", "text": "Ruby", "defaultCode": "class LFUCache\n\n=begin\n    :type capacity: Integer\n=end\n    def initialize(capacity)\n        \n    end\n\n\n=begin\n    :type key: Integer\n    :rtype: Integer\n=end\n    def get(key)\n        \n    end\n\n\n=begin\n    :type key: Integer\n    :type value: Integer\n    :rtype: Void\n=end\n    def put(key, value)\n        \n    end\n\n\nend\n\n# Your LFUCache object will be instantiated and called as such:\n# obj = LFUCache.new(capacity)\n# param_1 = obj.get(key)\n# obj.put(key, value)"}, {"value": "scala", "text": "Scala", "defaultCode": "class LFUCache(_capacity: Int) {\n\n    def get(key: Int): Int = {\n        \n    }\n\n    def put(key: Int, value: Int): Unit = {\n        \n    }\n\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * val obj = new LFUCache(capacity)\n * val param_1 = obj.get(key)\n * obj.put(key,value)\n */"}, {"value": "rust", "text": "Rust", "defaultCode": "struct LFUCache {\n\n}\n\n\n/** \n * `&self` means the method takes an immutable reference.\n * If you need a mutable reference, change it to `&mut self` instead.\n */\nimpl LFUCache {\n\n    fn new(capacity: i32) -> Self {\n        \n    }\n    \n    fn get(&self, key: i32) -> i32 {\n        \n    }\n    \n    fn put(&self, key: i32, value: i32) {\n        \n    }\n}\n\n/**\n * Your LFUCache object will be instantiated and called as such:\n * let obj = LFUCache::new(capacity);\n * let ret_1: i32 = obj.get(key);\n * obj.put(key, value);\n */"}, {"value": "racket", "text": "Racket", "defaultCode": "(define lfu-cache%\n  (class object%\n    (super-new)\n    \n    ; capacity : exact-integer?\n    (init-field\n      capacity)\n    \n    ; get : exact-integer? -> exact-integer?\n    (define/public (get key)\n      )\n    ; put : exact-integer? exact-integer? -> void?\n    (define/public (put key value)\n      )))\n\n;; Your lfu-cache% object will be instantiated and called as such:\n;; (define obj (new lfu-cache% [capacity capacity]))\n;; (define param_1 (send obj get key))\n;; (send obj put key value)"}, {"value": "erlang", "text": "Erlang", "defaultCode": "-spec lfu_cache_init_(Capacity :: integer()) -> any().\nlfu_cache_init_(Capacity) ->\n  .\n\n-spec lfu_cache_get(Key :: integer()) -> integer().\nlfu_cache_get(Key) ->\n  .\n\n-spec lfu_cache_put(Key :: integer(), Value :: integer()) -> any().\nlfu_cache_put(Key, Value) ->\n  .\n\n\n%% Your functions will be called as such:\n%% lfu_cache_init_(Capacity),\n%% Param_1 = lfu_cache_get(Key),\n%% lfu_cache_put(Key, Value),\n\n%% lfu_cache_init_ will be called before every test case, in which you can do some necessary initializations."}, {"value": "elixir", "text": "Elixir", "defaultCode": "defmodule LFUCache do\n  @spec init_(capacity :: integer) :: any\n  def init_(capacity) do\n    \n  end\n\n  @spec get(key :: integer) :: integer\n  def get(key) do\n    \n  end\n\n  @spec put(key :: integer, value :: integer) :: any\n  def put(key, value) do\n    \n  end\nend\n\n# Your functions will be called as such:\n# LFUCache.init_(capacity)\n# param_1 = LFUCache.get(key)\n# LFUCache.put(key, value)\n\n# LFUCache.init_ will be called before every test case, in which you can do some necessary initializations."}]
{
    "classname": "LFUCache",
    "maxbytesperline": 200000,
    "constructor": {
        "params": [
            {
                "type": "integer",
                "name": "capacity"
            }
        ]
    },
    "methods": [
        {
            "name" : "get",
            "params": [
                {
                    "type": "integer",
                    "name": "key"
                }
            ],
            "return": {
                "type": "integer"
            }
        },
        {
            "name" : "put",
            "params": [
                {
                    "type": "integer",
                    "name": "key"
                },
                {
                    "type": "integer",
                    "name": "value"
                }
            ],
            "return": {
                "type": "void"
            }
        }
    ],
    "systemdesign": true,
    "params": [
        {
            "name": "inputs",
            "type": "integer[]"
        },
        {
            "name": "inputs",
            "type": "integer[]"
        }
    ],
    "return": {
        "type": "list<String>",
        "dealloc": true
    }
}
{"cpp": ["C++", "<p>Compiled with <code> clang 19 </code> using the latest C++ 23 standard, and <code>libstdc++</code> provided by GCC 14.</p>\r\n\r\n<p>Your code is compiled with level two optimization (<code>-O2</code>). <a href=\"https://github.com/google/sanitizers/wiki/AddressSanitizer\" target=\"_blank\">AddressSanitizer</a> is also enabled to help detect out-of-bounds and use-after-free bugs.</p>\r\n\r\n<p>Most standard library headers are already included automatically for your convenience.</p>"], "java": ["Java", "<p><code>OpenJDK 21</code>. Using compile arguments: <code>--enable-preview --release 21</code></p>\r\n\r\n<p>Most standard library headers are already included automatically for your convenience.</p>\r\n<p>Includes <code>Pair</code> class from https://docs.oracle.com/javase/8/javafx/api/javafx/util/Pair.html.</p>"], "python": ["Python", "<p><code>Python 2.7.18</code>.</p>\r\n\r\n<p>Most libraries are already imported automatically for your convenience, such as <a href=\"https://docs.python.org/2/library/array.html\" target=\"_blank\">array</a>, <a href=\"https://docs.python.org/2/library/bisect.html\" target=\"_blank\">bisect</a>, <a href=\"https://docs.python.org/2/library/collections.html\" target=\"_blank\">collections</a>. If you need more libraries, you can import it yourself.</p>\r\n\r\n<p>For Map/TreeMap data structure, you may use <a href=\"http://www.grantjenks.com/docs/sortedcontainers/\" target=\"_blank\">sortedcontainers</a> library.</p>\r\n\r\n<p>Note that Python 2.7 <a href=\"https://www.python.org/dev/peps/pep-0373/\" target=\"_blank\">is not maintained anymore</a>. For the latest Python, please choose Python3 instead.</p>"], "c": ["C", "<p>Compiled with <code>gcc 14</code> using the gnu11 standard.</p>\r\n\r\n<p>Your code is compiled with level one optimization (<code>-O2</code>). <a href=\"https://github.com/google/sanitizers/wiki/AddressSanitizer\" target=\"_blank\">AddressSanitizer</a> is also enabled to help detect out-of-bounds and use-after-free bugs.</p>\r\n\r\n<p>Most standard library headers are already included automatically for your convenience.</p>\r\n\r\n<p>For hash table operations, you may use <a href=\"https://troydhanson.github.io/uthash/\" target=\"_blank\">uthash</a>. \"uthash.h\" is included by default. Below are some examples:</p>\r\n\r\n<p><b>1. Adding an item to a hash.</b>\r\n<pre>\r\nstruct hash_entry {\r\n    int id;            /* we'll use this field as the key */\r\n    char name[10];\r\n    UT_hash_handle hh; /* makes this structure hashable */\r\n};\r\n\r\nstruct hash_entry *users = NULL;\r\n\r\nvoid add_user(struct hash_entry *s) {\r\n    HASH_ADD_INT(users, id, s);\r\n}\r\n</pre>\r\n</p>\r\n\r\n<p><b>2. Looking up an item in a hash:</b>\r\n<pre>\r\nstruct hash_entry *find_user(int user_id) {\r\n    struct hash_entry *s;\r\n    HASH_FIND_INT(users, &user_id, s);\r\n    return s;\r\n}\r\n</pre>\r\n</p>\r\n\r\n<p><b>3. Deleting an item in a hash:</b>\r\n<pre>\r\nvoid delete_user(struct hash_entry *user) {\r\n    HASH_DEL(users, user);  \r\n}\r\n</pre>\r\n</p>"], "csharp": ["C#", "<p><a href=\"https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13\" target=\"_blank\">C# 13</a> with .NET 9 runtime</p>"], "javascript": ["JavaScript", "<p><code>Node.js 22.14.0</code>.</p>\r\n\r\n<p>Your code is run with <code>--harmony</code> flag, enabling <a href=\"http://node.green/\" target=\"_blank\">new ES6 features</a>.</p>\r\n\r\n<p><a href=\"https://lodash.com\" target=\"_blank\">lodash.js</a> library is included by default.</p>\r\n\r\n<p>For Priority Queue / Queue data structures, you may use 6.3.2 version of <a href=\"https://github.com/datastructures-js/priority-queue/tree/v6.3.2\" target=\"_blank\">datastructures-js/priority-queue</a> and 4.2.3 version of <a href=\"https://github.com/datastructures-js/queue/tree/v4.2.3\" target=\"_blank\">datastructures-js/queue</a> and 1.0.4 version of <a href=\"https://github.com/datastructures-js/deque/tree/v1.0.4\" target=\"_blank\">datastructures-js/deque</a>.</p>"], "ruby": ["Ruby", "<p><code>Ruby 3.2</code></p>\r\n\r\n<p>Some common data structure implementations are provided in the Algorithms module: https://www.rubydoc.info/github/kanwei/algorithms/Algorithms</p>"], "swift": ["Swift", "<p><code>Swift 6.0</code>.</p>\r\n\r\n<p>You may use the following packages:<br/>\r\n<a href=\"https://github.com/apple/swift-algorithms/tree/1.2.0\" target=\"_blank\">swift-algorithms 1.2.0</a><br/>\r\n<a href=\"https://github.com/apple/swift-collections/tree/1.1.4\" target=\"_blank\">swift-collections 1.1.4</a><br/>\r\n<a href=\"https://github.com/apple/swift-numerics/tree/1.0.2\" target=\"_blank\">swift-numerics 1.0.2</a></p>"], "golang": ["Go", "<p><code>Go 1.23</code></p>\r\n<p>Support <a href=\"https://pkg.go.dev/github.com/emirpasic/gods@v1.18.1\" target=\"_blank\">https://pkg.go.dev/github.com/emirpasic/gods@v1.18.1</a> and <a href=\"https://pkg.go.dev/github.com/emirpasic/gods/v2@v2.0.0-alpha\" target=\"_blank\">https://pkg.go.dev/github.com/emirpasic/gods/v2@v2.0.0-alpha</a> library.</p>"], "python3": ["Python3", "<p><code>Python 3.11</code>.</p>\r\n\r\n<p>Most libraries are already imported automatically for your convenience, such as <a href=\"https://docs.python.org/3/library/array.html\" target=\"_blank\">array</a>, <a href=\"https://docs.python.org/3/library/bisect.html\" target=\"_blank\">bisect</a>, <a href=\"https://docs.python.org/3/library/collections.html\" target=\"_blank\">collections</a>. If you need more libraries, you can import it yourself.</p>\r\n\r\n<p>For Map/TreeMap data structure, you may use <a href=\"http://www.grantjenks.com/docs/sortedcontainers/\" target=\"_blank\">sortedcontainers</a> library.</p>"], "scala": ["Scala", "<p><code>Scala 3.3.1</code>.</p>"], "kotlin": ["Kotlin", "<p><code>Kotlin 2.1.10</code>.</p>"], "rust": ["Rust", "<p><code>Rust 1.85.0</code>. Your code will be compiled with <code>opt-level</code> 2.</p>\r\n\r\n<p>Supports <a href=\"https://crates.io/crates/rand\" target=\"_blank\">rand v0.8</a> and <a href=\"https://crates.io/crates/regex\" target=\"_blank\">regex\u00a0v1</a> and <a href=\"https://crates.io/crates/itertools\" target=\"_blank\">itertools\u00a0v0.14</a> from crates.io</p>"], "php": ["PHP", "<p><code>PHP 8.2</code>.</p>\r\n<p>With bcmath module</p>"], "typescript": ["Typescript", "<p><code>TypeScript 5.7.3, Node.js 22.14.0</code>.</p>\r\n\r\n<p>Compile Options: <code>--alwaysStrict --strictBindCallApply --strictFunctionTypes --target ES2024</code></p>\r\n\r\n<p><a href=\"https://lodash.com\" target=\"_blank\">lodash.js</a> library is included by default.</p>\r\n\r\n<p>For Priority Queue / Queue data structures, you may use 6.3.2 version of <a href=\"https://github.com/datastructures-js/priority-queue/tree/v6.3.2\" target=\"_blank\">datastructures-js/priority-queue</a> and 4.2.3 version of <a href=\"https://github.com/datastructures-js/queue/tree/v4.2.3\" target=\"_blank\">datastructures-js/queue</a> and 1.0.4 version of <a href=\"https://github.com/datastructures-js/deque/tree/v1.0.4\" target=\"_blank\">datastructures-js/deque</a>.</p>"], "racket": ["Racket", "<p><a href=\"https://docs.racket-lang.org/guide/performance.html#%28tech._c%29\" target=\"_blank\">Racket CS</a> v8.15</p>\r\n\r\n<p>Using <code>#lang racket</code></p>\r\n\r\n<p>Required <code>data/gvector data/queue data/order data/heap</code> automatically for your convenience</p>"], "erlang": ["Erlang", "Erlang/OTP 26"], "elixir": ["Elixir", "Elixir 1.17 with Erlang/OTP 26"], "dart": ["Dart", "<p>Dart 3.2. You may use package <a href=\"https://pub.dev/packages/collection/versions/1.18.0\" target=\"_blank\">collection</a></p>\r\n\r\n<p>Your code will be run directly without compiling</p>"]}
['Hash Table', 'Linked List', 'Design', 'Doubly-Linked List']