feat: improve the Armstrong Number algorithm (TheAlgorithms#2480)

Co-authored-by: realstealthninja <[email protected]>

Author: Panquesito7

dynamic_programming/armstrong_number.cpp

@@ -1,39 +1,93 @@
-// Program to check whether a number is an armstrong number or not
-#include <cmath>
-#include <iostream>
-using std::cin;
-using std::cout;
+/**
+ * @file
+ * @brief Checks whether a number is an [Armstrong
+ * Number](https://en.wikipedia.org/wiki/Narcissistic_number) or not.
+ *
+ * @details
+ * An Armstrong number is a number that is the sum of its own digits each raised
+ * to the power of the number of digits. For example: 153 is an Armstrong number
+ * since 153 = 1^3 + 5^3 + 3^3.
+ *
+ * A few examples of valid armstrong numbers:
+ * 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 153, 370, 371, 407, 1634, 8208, 9474, 54748,
+ * 92727, 93084.
+ *
+ * Armstrong numbers are also known as Narcissistic Numbers, as stated in
+ * Wikipedia.
+ *
+ * @author [Shivam Singhal](https://github.com/shivhek25)
+ * @author [David Leal](https://github.com/Panquesito7)
+ */
 
-int main() {
-    int n = 0, temp = 0, rem = 0, count = 0, sum = 0;
-    cout << "Enter a number: ";
-    cin >> n;
+#include <cassert>   /// for assert
+#include <cmath>     /// for std::pow
+#include <iostream>  /// for IO operations
+
+/**
+ * @namespace
+ * @brief Dynamic Programming algorithms
+ */
+namespace dynamic_programming {
 
-    temp = n;
+/**
+ * @brief Checks if the given number is armstrong or not.
+ * @param number the number to check
+ * @returns false if the given number is NOT armstrong
+ * @returns true if the given number IS armstrong
+ */
+template <typename T>
+bool is_armstrong(const T &number) {
+    int count = 0, temp = number, result = 0, rem = 0;
 
-    /* First Count the number of digits
-       in the given number */
+    // Count the number of digits of the given number.
+    // For example: 153 would be 3 digits.
     while (temp != 0) {
         temp /= 10;
         count++;
     }
 
-    /* Calculation for checking of armstrongs number i.e.
-       in an n-digit number sum of the digits is raised to a power of n
-       is equal to the original number */
-
-    temp = n;
+    // Calculation for checking of armstrongs number i.e.
+    // in an n-digit number sum of the digits is raised to a power of `n` is
+    // equal to the original number.
+    temp = number;
     while (temp != 0) {
         rem = temp % 10;
-        sum += static_cast<int>(pow(rem, count));
+        result += static_cast<T>(std::pow(rem, count));
         temp /= 10;
     }
 
-    if (sum == n) {
-        cout << n << " is an armstrong number";
+    if (result == number) {
+        return true;
     } else {
-        cout << n << " is not an armstrong number";
+        return false;
     }
+}
+}  // namespace dynamic_programming
 
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void tests() {
+    assert(dynamic_programming::is_armstrong(153) == true);
+    assert(dynamic_programming::is_armstrong(1) == true);
+    assert(dynamic_programming::is_armstrong(0) == true);
+    assert(dynamic_programming::is_armstrong(370) == true);
+    assert(dynamic_programming::is_armstrong(1634) == true);
+    assert(dynamic_programming::is_armstrong(580) == false);
+    assert(dynamic_programming::is_armstrong(15) == false);
+    assert(dynamic_programming::is_armstrong(1024) == false);
+    assert(dynamic_programming::is_armstrong(989) == false);
+    assert(dynamic_programming::is_armstrong(103) == false);
+
+    std::cout << "All tests have successfully passed!\n";
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+    tests();  // run self-test implementations
     return 0;
 }