Random Pick with Weight
<p>You are given a <strong>0-indexed</strong> array of positive integers <code>w</code> where <code>w[i]</code> describes the <strong>weight</strong> of the <code>i<sup>th</sup></code> index.</p>

<p>You need to implement the function <code>pickIndex()</code>, which <strong>randomly</strong> picks an index in the range <code>[0, w.length - 1]</code> (<strong>inclusive</strong>) and returns it. The <strong>probability</strong> of picking an index <code>i</code> is <code>w[i] / sum(w)</code>.</p>

<ul>
	<li>For example, if <code>w = [1, 3]</code>, the probability of picking index <code>0</code> is <code>1 / (1 + 3) = 0.25</code> (i.e., <code>25%</code>), and the probability of picking index <code>1</code> is <code>3 / (1 + 3) = 0.75</code> (i.e., <code>75%</code>).</li>
</ul>

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

<pre>
<strong>Input</strong>
[&quot;Solution&quot;,&quot;pickIndex&quot;]
[[[1]],[]]
<strong>Output</strong>
[null,0]

<strong>Explanation</strong>
Solution solution = new Solution([1]);
solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input</strong>
[&quot;Solution&quot;,&quot;pickIndex&quot;,&quot;pickIndex&quot;,&quot;pickIndex&quot;,&quot;pickIndex&quot;,&quot;pickIndex&quot;]
[[[1,3]],[],[],[],[],[]]
<strong>Output</strong>
[null,1,1,1,1,0]

<strong>Explanation</strong>
Solution solution = new Solution([1, 3]);
solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4.
solution.pickIndex(); // return 1
solution.pickIndex(); // return 1
solution.pickIndex(); // return 1
solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4.

Since this is a randomization problem, multiple answers are allowed.
All of the following outputs can be considered correct:
[null,1,1,1,1,0]
[null,1,1,1,1,1]
[null,1,1,1,0,0]
[null,1,1,1,0,1]
[null,1,0,1,0,0]
......
and so on.
</pre>

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

<ul>
	<li><code>1 &lt;= w.length &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= w[i] &lt;= 10<sup>5</sup></code></li>
	<li><code>pickIndex</code> will be called at most <code>10<sup>4</sup></code> times.</li>
</ul>

['random-pick-index', 'random-pick-with-blacklist', 'random-point-in-non-overlapping-rectangles']
[]
[{"value": "cpp", "text": "C++", "defaultCode": "class Solution {\npublic:\n    Solution(vector<int>& w) {\n        \n    }\n    \n    int pickIndex() {\n        \n    }\n};\n\n/**\n * Your Solution object will be instantiated and called as such:\n * Solution* obj = new Solution(w);\n * int param_1 = obj->pickIndex();\n */"}, {"value": "java", "text": "Java", "defaultCode": "class Solution {\n\n    public Solution(int[] w) {\n        \n    }\n    \n    public int pickIndex() {\n        \n    }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * Solution obj = new Solution(w);\n * int param_1 = obj.pickIndex();\n */"}, {"value": "python", "text": "Python", "defaultCode": "class Solution(object):\n\n    def __init__(self, w):\n        \"\"\"\n        :type w: List[int]\n        \"\"\"\n        \n\n    def pickIndex(self):\n        \"\"\"\n        :rtype: int\n        \"\"\"\n        \n\n\n# Your Solution object will be instantiated and called as such:\n# obj = Solution(w)\n# param_1 = obj.pickIndex()"}, {"value": "python3", "text": "Python3", "defaultCode": "class Solution:\n\n    def __init__(self, w: List[int]):\n        \n\n    def pickIndex(self) -> int:\n        \n\n\n# Your Solution object will be instantiated and called as such:\n# obj = Solution(w)\n# param_1 = obj.pickIndex()"}, {"value": "c", "text": "C", "defaultCode": "\n\n\ntypedef struct {\n    \n} Solution;\n\n\nSolution* solutionCreate(int* w, int wSize) {\n    \n}\n\nint solutionPickIndex(Solution* obj) {\n    \n}\n\nvoid solutionFree(Solution* obj) {\n    \n}\n\n/**\n * Your Solution struct will be instantiated and called as such:\n * Solution* obj = solutionCreate(w, wSize);\n * int param_1 = solutionPickIndex(obj);\n \n * solutionFree(obj);\n*/"}, {"value": "csharp", "text": "C#", "defaultCode": "public class Solution {\n\n    public Solution(int[] w) {\n        \n    }\n    \n    public int PickIndex() {\n        \n    }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * Solution obj = new Solution(w);\n * int param_1 = obj.PickIndex();\n */"}, {"value": "javascript", "text": "JavaScript", "defaultCode": "/**\n * @param {number[]} w\n */\nvar Solution = function(w) {\n    \n};\n\n/**\n * @return {number}\n */\nSolution.prototype.pickIndex = function() {\n    \n};\n\n/** \n * Your Solution object will be instantiated and called as such:\n * var obj = new Solution(w)\n * var param_1 = obj.pickIndex()\n */"}, {"value": "typescript", "text": "TypeScript", "defaultCode": "class Solution {\n    constructor(w: number[]) {\n        \n    }\n\n    pickIndex(): number {\n        \n    }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * var obj = new Solution(w)\n * var param_1 = obj.pickIndex()\n */"}, {"value": "php", "text": "PHP", "defaultCode": "class Solution {\n    /**\n     * @param Integer[] $w\n     */\n    function __construct($w) {\n        \n    }\n  \n    /**\n     * @return Integer\n     */\n    function pickIndex() {\n        \n    }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * $obj = Solution($w);\n * $ret_1 = $obj->pickIndex();\n */"}, {"value": "swift", "text": "Swift", "defaultCode": "\nclass Solution {\n\n    init(_ w: [Int]) {\n        \n    }\n    \n    func pickIndex() -> Int {\n        \n    }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * let obj = Solution(w)\n * let ret_1: Int = obj.pickIndex()\n */"}, {"value": "kotlin", "text": "Kotlin", "defaultCode": "class Solution(w: IntArray) {\n\n    fun pickIndex(): Int {\n        \n    }\n\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * var obj = Solution(w)\n * var param_1 = obj.pickIndex()\n */"}, {"value": "dart", "text": "Dart", "defaultCode": "class Solution {\n\n  Solution(List<int> w) {\n    \n  }\n  \n  int pickIndex() {\n    \n  }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * Solution obj = Solution(w);\n * int param1 = obj.pickIndex();\n */"}, {"value": "golang", "text": "Go", "defaultCode": "type Solution struct {\n    \n}\n\n\nfunc Constructor(w []int) Solution {\n    \n}\n\n\nfunc (this *Solution) PickIndex() int {\n    \n}\n\n\n/**\n * Your Solution object will be instantiated and called as such:\n * obj := Constructor(w);\n * param_1 := obj.PickIndex();\n */"}, {"value": "ruby", "text": "Ruby", "defaultCode": "class Solution\n\n=begin\n    :type w: Integer[]\n=end\n    def initialize(w)\n        \n    end\n\n\n=begin\n    :rtype: Integer\n=end\n    def pick_index()\n        \n    end\n\n\nend\n\n# Your Solution object will be instantiated and called as such:\n# obj = Solution.new(w)\n# param_1 = obj.pick_index()"}, {"value": "scala", "text": "Scala", "defaultCode": "class Solution(_w: Array[Int]) {\n\n    def pickIndex(): Int = {\n        \n    }\n\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * val obj = new Solution(w)\n * val param_1 = obj.pickIndex()\n */"}, {"value": "rust", "text": "Rust", "defaultCode": "struct Solution {\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 Solution {\n\n    fn new(w: Vec<i32>) -> Self {\n        \n    }\n    \n    fn pick_index(&self) -> i32 {\n        \n    }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * let obj = Solution::new(w);\n * let ret_1: i32 = obj.pick_index();\n */"}, {"value": "racket", "text": "Racket", "defaultCode": "(define solution%\n  (class object%\n    (super-new)\n    \n    ; w : (listof exact-integer?)\n    (init-field\n      w)\n    \n    ; pick-index : -> exact-integer?\n    (define/public (pick-index)\n      )))\n\n;; Your solution% object will be instantiated and called as such:\n;; (define obj (new solution% [w w]))\n;; (define param_1 (send obj pick-index))"}, {"value": "erlang", "text": "Erlang", "defaultCode": "-spec solution_init_(W :: [integer()]) -> any().\nsolution_init_(W) ->\n  .\n\n-spec solution_pick_index() -> integer().\nsolution_pick_index() ->\n  .\n\n\n%% Your functions will be called as such:\n%% solution_init_(W),\n%% Param_1 = solution_pick_index(),\n\n%% solution_init_ will be called before every test case, in which you can do some necessary initializations."}, {"value": "elixir", "text": "Elixir", "defaultCode": "defmodule Solution do\n  @spec init_(w :: [integer]) :: any\n  def init_(w) do\n    \n  end\n\n  @spec pick_index() :: integer\n  def pick_index() do\n    \n  end\nend\n\n# Your functions will be called as such:\n# Solution.init_(w)\n# param_1 = Solution.pick_index()\n\n# Solution.init_ will be called before every test case, in which you can do some necessary initializations."}]
{
    "classname": "Solution",
    "maxbytesperline": 200000,
    "constructor": {
        "params": [
            {
                "name": "w",
                "type": "integer[]"
            },
            {
                "name": "wSize",
                "type": "integer",
                "lang": "c",
                "value": "size_1"
            }
        ]
    },
    "methods": [
        {
            "name" : "pickIndex",
            "params": [
            ],
            "return": {
                "type": "integer"
            }
        }
    ],
    "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>"]}
['Array', 'Math', 'Binary Search', 'Prefix Sum', 'Randomized']