Add Armstrong Numbers (rust-lang#305)

Author: Sedat Aybars Nazlica

DIRECTORY.md

@@ -69,6 +69,7 @@
     * [Pollard's Rho algorithm](https://github.com/TheAlgorithms/Rust/blob/master/src/math/pollard_rho.rs)
     * [Simpson's Rule](https://github.com/TheAlgorithms/Rust/blob/master/src/math/simpson_integration.rs)
     * [Fast Fourier Transform](https://github.com/TheAlgorithms/Rust/blob/master/src/math/fast_fourier_transform.rs)
+    * [Armstrong Number](https://github.com/TheAlgorithms/Rust/blob/master/src/math/armstrong_number.rs)
   * Searching
     * [Binary Search](https://github.com/TheAlgorithms/Rust/blob/master/src/searching/binary_search.rs)
     * [Binary Search Recursive](https://github.com/TheAlgorithms/Rust/blob/master/src/searching/binary_search_recursive.rs)

README.md

@@ -53,6 +53,7 @@ These are for demonstration purposes only.
 - [x] [Pollard's Rho algorithm](./src/math/pollard_rho.rs)
 - [x] [Simpson's Rule for Integration](./src/math/simpson_integration.rs)
 - [x] [Fast Fourier Transform](./src/math/fast_fourier_transform.rs)
+- [x] [Armstrong Number](./src/math/armstrong_number.rs)
 
 ## [Dynamic Programming](./src/dynamic_programming)
 

src/math/armstrong_number.rs

@@ -0,0 +1,44 @@
+pub fn is_armstrong_number(number: u32) -> bool {
+    let mut digits: Vec<u32> = Vec::new();
+    let mut num: u32 = number;
+
+    loop {
+        digits.push(num % 10);
+        num /= 10;
+        if num == 0 {
+            break;
+        }
+    }
+
+    let sum_nth_power_of_digits: u32 = digits
+        .iter()
+        .map(|digit| digit.pow(digits.len() as u32))
+        .sum();
+    sum_nth_power_of_digits == number
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn one_digit_armstrong_number() {
+        assert!(is_armstrong_number(1))
+    }
+    #[test]
+    fn two_digit_numbers_are_not_armstrong_numbers() {
+        assert!(!is_armstrong_number(15))
+    }
+    #[test]
+    fn three_digit_armstrong_number() {
+        assert!(is_armstrong_number(153))
+    }
+    #[test]
+    fn three_digit_non_armstrong_number() {
+        assert!(!is_armstrong_number(105))
+    }
+    #[test]
+    fn big_armstrong_number() {
+        assert!(is_armstrong_number(912985153))
+    }
+}

src/math/mod.rs

@@ -1,3 +1,4 @@
+mod armstrong_number;
 mod baby_step_giant_step;
 mod extended_euclidean_algorithm;
 mod fast_fourier_transform;
@@ -17,6 +18,7 @@ mod simpson_integration;
 mod square_root;
 mod trial_division;
 
+pub use self::armstrong_number::is_armstrong_number;
 pub use self::baby_step_giant_step::baby_step_giant_step;
 pub use self::extended_euclidean_algorithm::extended_euclidean_algorithm;
 pub use self::fast_fourier_transform::{