Solve LeetCode #9 'Palindrome Number' [Easy].

LeetCode/src/LeetCode.Challenges/Problems0XX/P009_PalindromeNumber/Solution.cs

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+namespace LeetCode.Challenges.Problems0XX.P009_PalindromeNumber;
+
+public static class Solution
+{
+    public static bool IsPalindrome(int x)
+    {
+        if (x < 0 || (x % 10 == 0 && x != 0))
+        {
+            return false;
+        }
+
+        List<int> digits = [];
+        while (x >= 1)
+        {
+            digits.Add(x % 10);
+            x /= 10;
+        }
+
+        var left = 0;
+        var right = digits.Count - 1;
+
+        while (left <= right)
+        {
+            if (digits[left] != digits[right])
+            {
+                return false;
+            }
+
+            left++;
+            right--;
+        }
+
+        return true;
+    }
+}

LeetCode/tests/LeetCode.Challenges.UnitTests/Problems0XX/P009_PalindromeNumber/SolutionTests.cs

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+using FluentAssertions;
+using LeetCode.Challenges.Problems0XX.P009_PalindromeNumber;
+using Shouldly;
+using Xunit;
+
+namespace LeetCode.Challenges.UnitTests.Problems0XX.P009_PalindromeNumber;
+
+public class SolutionTests
+{
+    [Theory]
+    [MemberData(nameof(TestData))]
+    public void GivenNumber_WhenCallIsPalindrome_ThenResultAsExpected(int number, bool expectedResult)
+    {
+        Solution.IsPalindrome(number).ShouldBe(expectedResult);
+    }
+
+    public static IEnumerable<object[]> TestData()
+    {
+        yield return [1, true];
+        yield return [11, true];
+        yield return [121, true];
+        yield return [12321, true];
+        yield return [12, false];
+        yield return [123, false];
+        yield return [-121, false];
+    }
+}