chore: import upstream snapshot with attribution

math/check_amicable_pair.cpp

@@ -0,0 +1,84 @@
+/**
+ * @file
+ * @brief A C++ Program to check whether a pair of numbers is an [amicable
+ * pair](https://en.wikipedia.org/wiki/Amicable_numbers) or not.
+ *
+ * @details
+ * An Amicable Pair is two positive integers such that the sum of the proper
+ * divisor for each number is equal to the other number.
+ *
+ * @note Remember that a proper divisor is any positive whole number that
+ * divides into a selected number, apart from the selected number itself, and
+ * returns a positive integer. for example 1, 2 and  5 are all proper divisors
+ * of 10.
+ *
+ * @author [iamnambiar](https://github.com/iamnambiar)
+ */
+#include <cassert>   /// for assert
+#include <iostream>  /// for IO operations
+
+/**
+ * @brief Mathematical algorithms
+ * @namespace
+ */
+namespace math {
+/**
+ * @brief Function to calculate the sum of all the proper divisor
+ * of an integer.
+ * @param num selected number.
+ * @return Sum of the proper divisor of the number.
+ */
+int sum_of_divisor(int num) {
+    // Variable to store the sum of all proper divisors.
+    int sum = 1;
+    // Below loop condition helps to reduce Time complexity by a factor of
+    // square root of the number.
+    for (int div = 2; div * div <= num; ++div) {
+        // Check 'div' is divisor of 'num'.
+        if (num % div == 0) {
+            // If both divisor are same, add once to 'sum'
+            if (div == (num / div)) {
+                sum += div;
+            } else {
+                // If both divisor are not the same, add both to 'sum'.
+                sum += (div + (num / div));
+            }
+        }
+    }
+    return sum;
+}
+
+/**
+ * @brief Function to check whether the pair is amicable or not.
+ * @param x First number.
+ * @param y Second number.
+ * @return `true` if the pair is amicable
+ * @return `false` if the pair is not amicable
+ */
+bool are_amicable(int x, int y) {
+    return (sum_of_divisor(x) == y) && (sum_of_divisor(y) == x);
+}
+}  // namespace math
+
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void tests() {
+    assert(math::are_amicable(220, 284) == true);
+    assert(math::are_amicable(6368, 6232) == true);
+    assert(math::are_amicable(458, 232) == false);
+    assert(math::are_amicable(17296, 18416) == true);
+    assert(math::are_amicable(18416, 17296) == true);
+
+    std::cout << "All tests have successfully passed!" << std::endl;
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+    tests();  // perform self-tests implementations
+    return 0;
+}