PowerDMS_Interview.cs

using System.Collections.Generic;
using System.Linq;

namespace PowerDMS.Main
{
    public class Interview
    {
        /// <summary>
        /// Compares two strings for an anagram
        /// </summary>
        /// <param name="str1">First string for comparison</param>
        /// <param name="str2">Second string for comparison</param>
        /// <returns>True if the two strings form an anagram, otherwise false</returns>
        public bool IsAnagram(string str1, string str2)
        {
            // **Assumption** Leading/trailing whitespace is acceptable input, but not considered for comparison.
            str1 = str1.Trim();
            str2 = str2.Trim();

            // internal whitespace breaks the definition of an anagram
            if (str1.Any(char.IsWhiteSpace) || str2.Any(char.IsWhiteSpace))
            {
                return false;
            }

            // null strings break the definition of an anagram
            if (string.IsNullOrWhiteSpace(str1) || string.IsNullOrWhiteSpace(str2))
            {
                return false;
            }

            var str1CharCounts = TallyChars(str1);
            var str2CharCounts = TallyChars(str2);

            // check for differring keys and key counts
            if (str1CharCounts.Count != str2CharCounts.Count ||
                !str1CharCounts.Keys.All(x => str2CharCounts.ContainsKey(x)))
            {
                return false;
            }

            foreach (var (key, value) in str1CharCounts)
            {
                if (str2CharCounts[key] != value)
                {
                    return false;
                }
            }

            return true;
        }

        /// <summary>
        /// Counts the occurrence of each letter in a given string
        /// </summary>
        /// <param name="str">The string containing characters to tally</param>
        /// <returns>A Dictionary mapping the letters that occurred in the string to the total number of times that they occurred in the string</returns>
        public Dictionary<char, int> TallyChars(string str)
        {
            var chars = str.ToCharArray(0, str.Length);
            var map = new Dictionary<char, int>();
            foreach (var c in chars)
            {
                if (map.TryGetValue(c, out var currentCount))
                {
                    map[c] = currentCount + 1;
                }
                else
                {
                    map.Add(c, 1);
                }
            }

            return map;
        }
    }
}

PowerDMS_Interview_Tests.cs

using FluentAssertions;
using PowerDMS.Main;
using Xunit;

namespace PowerDMS.Tests
{
    public class InterviewTests
    {
        private Interview Interview { get; }

        public InterviewTests()
        {
            Interview = new Interview();
        }

        [Fact]
        public void Returns_True_If_Anagram()
        {
            var str1 = "cinema";
            var str2 = "iceman";
            Interview.IsAnagram(str1, str2).Should().BeTrue();
        }

        [Fact]
        public void Returns_False_If_Two_Strings_Have_Same_Length_Different_Letters()
        {
            var str1 = "ars";
            var str2 = "set";

            Interview.IsAnagram(str1, str2).Should().BeFalse();
        }

        [Fact]
        public void Returns_False_If_Two_Strings_Have_Differring_Lengths()
        {
            var str1 = "arst";
            var str2 = "qw";

            Interview.IsAnagram(str1, str2).Should().BeFalse();
        }

        [Fact]
        public void Returns_False_If_Strings_Have_Same_Letters_Different_Count()
        {
            var str1 = "aarr";
            var str2 = "arrr";

            Interview.IsAnagram(str1, str2).Should().BeFalse();
        }

        [Fact]
        public void Returns_False_If_Strings_Contain_Whitespace()
        {
            var str1 = "aa rr";
            var str2 = "aa rr";

            Interview.IsAnagram(str1, str2).Should().BeFalse();
        }

        [Fact]
        public void Returns_False_If_String_Is_Whitespace()
        {
            var str1 = "";
            var str2 = "aarr";

            Interview.IsAnagram(str1, str2).Should().BeFalse();
        }

        [Fact]
        public void Leading_And_Trailing_Whitespace_Are_Acceptable()
        {
            var str1 = " arst";
            var str2 = "sart    ";

            Interview.IsAnagram(str1, str2).Should().BeTrue();
        }
    }
}