[Hacker Rank]: Warmup: Diagonal Difference. Solved ✅.

Author: Gonzalo Diaz

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 $

src/lib/exercises/include/exercises/hackerrank/warmup/diagonal_difference.hpp

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+#include <vector>
+
+#pragma once
+
+namespace hackerrank::warmup {
+    int diagonalDifference(const std::vector<std::vector<int>>& arr);
+}

src/lib/exercises/src/hackerrank/warmup/diagonal_difference.cpp

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+#include <exercises/hackerrank/warmup/diagonal_difference.hpp>
+
+/**
+ * @link Problem definition [[docs/hackerrank/warmup/diagonal_difference.md]]
+ */
+
+#include <numeric>
+#include <vector>
+
+namespace hackerrank::warmup {
+    int diagonalDifference(const std::vector<std::vector<int>>& arr) {
+        int diag1 = 0;
+        int diag2 = 0;
+        size_t last = arr.size() - 1L;
+
+        for (int i = 0; i < arr.size(); i++) {
+            for (int j = 0; j < arr[i].size(); j++) {
+                if (i == j) {
+                    diag1 += arr[i][j];
+                    diag2 += arr[last - i][j];
+                }
+            }
+        }
+        return abs(diag1 - diag2);
+    }
+}

src/tests/unit/lib/hackerrank/warmup/diagonal_difference.test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include <exercises/hackerrank/warmup/diagonal_difference.hpp>
+#include <iostream>
+#include <vector>
+
+#include <filesystem>
+#include <fstream>
+#include <nlohmann/json.hpp>
+using json = nlohmann::json;
+
+TEST_CASE("diagonalDifference JSON Test Cases", "[warmup]")
+{
+    std::filesystem::path cwd = std::filesystem::current_path();
+    std::string path = cwd.string() + "/unit/lib/hackerrank/warmup/diagonal_difference.testcases.json";
+
+    INFO("diagonalDifference JSON test cases FILE: " << path);
+
+    std::ifstream f(path);
+    json data = json::parse(f);
+
+    for (auto testcase : data) {
+        long result = hackerrank::warmup::diagonalDifference(testcase["matrix"]);
+        CHECK(result == testcase["expected"]);
+    }
+}

src/tests/unit/lib/hackerrank/warmup/diagonal_difference.testcases.json

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+[
+  { "matrix":
+    [
+      [11, 2, 4],
+      [4, 5, 6],
+      [10, 8, -12]
+    ],
+    "expected": 15
+  }
+]