using System;

using System.Collections.Generic;

using System.Linq;      

​

public class Solution {

    //Variables

    private Random rnd;

    private Dictionary<int, List<int>> numIndices;

    private List<int> numsList;

    public Solution(int[] nums) {

        rnd = new Random();

        numIndices = new Dictionary<int, List<int>>();

        numsList = new List<int>();

        //Adds nums to the numIndices where the int is the number and the List<int> is the indices of that num in nums

        for(int i = 0; i < nums.Length; i++)

        {

            //If the num does not exists - add to the dictionary

            if(!numIndices.ContainsKey(nums[i]))

            {

                numIndices.Add(nums[i], new List<int>());

            }

            numIndices[nums[i]].Add(i);

        }

    }

    public int Pick(int target) {

        //Picks a random index from numIndices

        int n = numIndices[target].Count;

        var res = numIndices[target];

        Console.WriteLine(res[rnd.Next(n)]);

        return res[rnd.Next(n)];

    }

}

​

​

public class Program

{

    public static void Main()

    {

        Solution solution = new Solution(new int[] {1, 2, 3, 3, 3});

        solution.Pick(3); // It should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.

        solution.Pick(1); // It should return 0. Since in the array only nums[0] is equal to 1.

        solution.Pick(3); // It should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.

        Console.WriteLine("Hello World");

    }

}