Program.cs

using System;
using System.Collections.Generic;

namespace ConsoleApp4
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, world!");

            // Write a program that prints the numbers from 1 to 100. 
            // But for multiples of three print “City” instead of the number and for the multiples of five print “Park”. 
            // For numbers which are multiples of both three and five print “CityPark”.
            for (var i = 1; i < 100; i++)
            {
                if (i % 3 == 0 && i % 5 == 0)
                {
                    Console.WriteLine("CityPark");
                }
                else if (i % 3 == 0)
                {
                    Console.WriteLine("City");
                }
                else if (i % 5 == 0)
                {
                    Console.WriteLine("Park");
                }
                else
                {
                    Console.WriteLine(i);
                }
            }

            // Given an array of integers with no duplicates, return indices of the two numbers such that they add up to a specific target.
            // You may assume that each input would have exactly one solution, and you may not use the same element twice.
            static string GetIndiciesThatAddToTarget(int[] items, int target)
            {
                var dictionary = new Dictionary<int,int>();

                int iCount = 0;
                foreach(var i in items)
                {
                    dictionary.Add(i, iCount);
                    iCount++;
                }

                int jCount = 0;
                foreach (var j in items)
                {
                    int missing = target - j;

                    bool found = dictionary.TryGetValue(missing, out int indice);

                    if(found)
                    {
                        return $"[{jCount}, {indice}]";
                    }

                    jCount++;
                }

                return "Target Unreachable";
            }

            var array = new int[] { 2, 7, 11, 15 };
            var target = 9;

            Console.WriteLine(GetIndiciesThatAddToTarget(array, target));
        }
    }
}