[Hacker Rank]: Diagonal Difference solved ✓

Author: Gonzalo Diaz

algorithm-exercises-csharp-test/src/hackerrank/warmup/DiagonalDifference.Test.cs

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+namespace algorithm_exercises_csharp.hackerrank;
+
+[TestClass]
+public class DiagonalDifferenceTest
+{
+  [TestMethod]
+  public void testDiagonalDifference()
+  {
+    List<List<int>> arr = [
+      [11, 2, 4],
+      [4, 5, 6],
+      [10, 8, -12]
+    ];
+    int expectedAnswer = 15;
+    int result = DiagonalDifference.diagonalDifference(arr);
+
+    Assert.AreEqual(expectedAnswer, result);
+  }
+}
+

algorithm-exercises-csharp/src/hackerrank/warmup/DiagonalDifference.cs

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+// @link Problem definition [[docs/hackerrank/warmup/diagonal_difference.md]]
+
+namespace algorithm_exercises_csharp.hackerrank;
+
+using System.Diagnostics.CodeAnalysis;
+
+public class DiagonalDifference
+{
+  [ExcludeFromCodeCoverage]
+  protected DiagonalDifference() { }
+
+  public static int diagonalDifference(List<List<int>> _arr)
+  {
+    int diag1 = 0;
+    int diag2 = 0;
+    int last = _arr.Count - 1;
+
+    int i = 0;
+    foreach (List<int> line in _arr)
+    {
+      int j = 0;
+      foreach (int cell in line)
+      {
+        if (i == j)
+        {
+          diag1 += cell;
+          diag2 += _arr[last - i][j];
+        }
+
+        j += 1;
+      }
+
+      i += 1;
+    }
+
+    int result = Math.Abs(diag1 - diag2);
+    return result;
+  }
+
+}

docs/hackerrank/warmup/diagonal_difference.md

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+# [Diagonal Difference](https://www.hackerrank.com/challenges/diagonal-difference)
+
+Difficulty: #easy
+Category: #warmup
+
+Given a square matrix, calculate the absolute difference between the sums
+of its diagonals.
+For example, the square matrix $ arr $ is shown below:
+
+```text
+1 2 3
+4 5 6
+9 8 9
+```
+
+The left-to-right $ diagonal = 1 + 5 + 9 = 15 $.
+The right to left $ diagonal = 3 + 5 + 9 = 17 $.
+Their absolute difference is $ |15 - 17| = 2 $.
+
+## Function description
+
+Complete the $ diagonalDifference $ function in the editor below.
+diagonalDifference takes the following parameter:
+
+- int ` arr[n][m] `: an array of integers
+
+## Return
+
+- int: the absolute diagonal difference
+
+## Input Format
+
+The first line contains a single integer, n, the number of
+rows and columns in the square matrix arr.
+Each of the next n lines describes a row, arr[i], and consists of
+space-separated integers ` arr[i][j] `.
+
+## Constraints
+
+$ -100 \leq $ ` arr[i][j] ` $ \leq 100 $
+
+## Output Format
+
+Return the absolute difference between the sums of the matrix's
+two diagonals as a single integer.
+
+## Sample Input
+
+```text
+3
+11 2 4
+4 5 6
+10 8 -12
+```
+
+Sample Output
+
+```text
+15
+```
+
+## Explanation
+
+The primary diagonal is:
+
+```text
+11
+   5
+     -12
+```
+
+Sum across the primary diagonal: 11 + 5 - 12 = 4
+The secondary diagonal is:
+
+```text
+     4
+   5
+10
+```
+
+Sum across the secondary diagonal: $ 4 + 5 + 10 = 19 $
+Difference: $ |4 - 19| = 15 $
+
+*Note*: $ |x| $ is the
+[absolute value](https://www.mathsisfun.com/numbers/absolute-value.html)
+of $ x $