Even Tree - study code - very readable code - https://www.hackerrank.com/rest/contests/master/challenges/even-tree/hackers/Misha2Kota/download_solution

EvenTreeStudy2.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;

namespace EvenTree
{
    class Solution
    {
        static List<Tuple<int, int>> edges = new List<Tuple<int, int>>();
        static int numVert;
        static Dictionary<int, List<int>> vertIndex = new Dictionary<int, List<int>>();

        static void Main(string[] args)
        {

            //Console.SetIn(File.OpenText(@"C:\Users\Misha2Kota\Documents\eventree.input"));

            numVert = Int32.Parse(Console.ReadLine().Split(' ')[0]);
            for (int i = 0; i < numVert; i++)
                vertIndex[i] = new List<int>();

            for (int i = 0; i < numVert - 1; ++i)
            {
                var vals = Console.ReadLine().Split(' ');
                int v1 = int.Parse(vals[0]) - 1;
                int v2 = int.Parse(vals[1]) - 1;
                edges.Add(Tuple.Create(v1, v2));

                vertIndex[v1].Add(v2);
                vertIndex[v2].Add(v1);
            }

            Console.WriteLine(Enumerable.Range(0, numVert - 1).Where(vert => canRemove(vert)).Count());
        }

        static bool canRemove(int edgeInd)
        {
            HashSet<int> touched = new HashSet<int>();
            Queue<int> verQ = new Queue<int>();

            var edgeUnderTest = edges[edgeInd];

            touched.Add(edgeUnderTest.Item1);
            touched.Add(edgeUnderTest.Item2);

            verQ.Enqueue(edgeUnderTest.Item2);
            while (verQ.Count > 0)
            {
                int vert = verQ.Dequeue();

                foreach (int connect in vertIndex[vert])
                {
                    if (!touched.Contains(connect))
                    {
                        touched.Add(connect);
                        verQ.Enqueue(connect);
                    }
                }
            }

            return touched.Count % 2 == 1;
        }
    }
}