using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        SortedList<int, string> planets = new SortedList<int, string>() {

            { 1, "Mercury" },

            { 2, "Venus" },

            { 3, "Earth" }

        };

​

        // Generate an exception if you try to modify the collection

        foreach (var planet in planets)

        {

            if (planet.Key == 2) // <--- RUN SOLUTION CODE BELOW. CHANGE 2 with 4

                planets.Remove(planet.Key); // Throw an exception here

        }

        //SOLUTION below

        // Copy the keys in a temp list and then iterate through this temp list to modify the collection:

​

        //Populate all the keys in a temp list

        var keys = new List<int>(planets.Keys); // Populated with 1, 2, 3

        // Iterate through keys and remove the item from the collection (planets)

        foreach (var key in keys)

        {

            if (key == 2)

                planets.Remove(key); // Removed { 2, Venus }

            if (planets.ContainsKey(key))

                Console.WriteLine($"{key}, {planets[key]}");

        }

    }

}