Added a run for the two-sum problem with reduced time complexity.

samples/Hussy.Net.Playground/Leetcode/Easy/TwoSum/ComplexityRun.cs

@@ -0,0 +1,39 @@
+using Glitter.Collections;
+
+namespace Hussy.Net.Playground.Leetcode.Easy;
+
+/// <summary>
+/// Represents a solution and its tests for the leetcode two-sum problem.
+/// </summary>
+/// <see href="https://leetcode.com/problems/two-sum/description/"/>
+public sealed partial class TwoSum
+{
+    /// <summary>
+    ///     A direct approach to solving the problem with less time complexity
+    ///     to understand where Hussy may be lacking.
+    /// </summary>
+    /// <param name="numbers">The array of numbers to look through.</param>
+    /// <param name="target">
+    ///     The target number which the two numbers in <paramref name="numbers"/> must add up to.
+    /// </param>
+    /// <returns>
+    ///     The two indices of the numbers which add up to the <paramref name="target"/>.
+    /// </returns>
+    private static IEnumerable<int> ComplexityRun(
+        int[] numbers,
+        int target)
+    {
+        var seen = new Dictionary<int, int>();
+        for (var i = 0; i < numbers.Length; i++)
+        {
+            var currentNumber = numbers[i];
+            var complement = target - currentNumber;
+            if (seen.TryGetValue(complement, out var value))
+                return [value, i];
+
+            seen[currentNumber] = i;
+        }
+
+        return Enumerable.Empty<int>();
+    }
+}

samples/Hussy.Net.Playground/Leetcode/Easy/TwoSum/Tests/Setup.cs

@@ -11,7 +11,8 @@ public sealed partial class TwoSum
     /// </summary>
     private static TestFunction[] TestFunctions =>
     [
-        DryRun
+        DryRun,
+        ComplexityRun
     ];
 
     /// <summary>
@@ -29,7 +30,7 @@ private static void RunTest(
             var resultingSequence = results.ToList();
 
             var excessResults = resultingSequence.Except(expectedSequence);
-            Assert.True(expectedSequence.All(resultingSequence.Contains));
+            Assert.True(expectedSequence.TrueForAll(resultingSequence.Contains));
             Assert.Empty(excessResults);
         }
     }