feat: add gcd_of_n_numbers (rust-lang#304)

Author: fffzlfk

README.md

@@ -41,6 +41,7 @@ These are for demonstration purposes only.
 - [x] [Baby-Step Giant-Step Algorithm](./src/math/baby_step_giant_step.rs)
 - [x] [Extended euclidean algorithm](./src/math/extended_euclidean_algorithm.rs)
 - [x] [Greatest common divisor](./src/math/greatest_common_divisor.rs)
+- [x] [Greatest common divisor of n numbers](./src/math/gcd_of_n_numbers.rs)
 - [x] [Miller Rabin primality test](./src/math/miller_rabin.rs)
 - [x] [Pascal's triangle](./src/math/pascal_triangle.rs)
 - [x] [Square root with Newton's method](./src/math/square_root.rs)

src/math/gcd_of_n_numbers.rs

@@ -0,0 +1,29 @@
+/// returns the greatest common divisor of n numbers
+pub fn gcd(nums: &[usize]) -> usize {
+    if nums.len() == 1 {
+        return nums[0];
+    }
+    let a = nums[0];
+    let b = gcd(&nums[1..]);
+    gcd_of_two_numbers(a, b)
+}
+
+fn gcd_of_two_numbers(a: usize, b: usize) -> usize {
+    if b == 0 {
+        return a;
+    }
+    gcd_of_two_numbers(b, a % b)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn it_works() {
+        assert_eq!(gcd(&[1, 2, 3, 4, 5]), 1);
+        assert_eq!(gcd(&[2, 4, 6, 8, 10]), 2);
+        assert_eq!(gcd(&[3, 6, 9, 12, 15]), 3);
+        assert_eq!(gcd(&[10]), 10);
+        assert_eq!(gcd(&[21, 110]), 1);
+    }
+}

src/math/mod.rs

@@ -2,6 +2,7 @@ mod baby_step_giant_step;
 mod extended_euclidean_algorithm;
 mod fast_fourier_transform;
 mod fast_power;
+mod gcd_of_n_numbers;
 mod greatest_common_divisor;
 mod linear_sieve;
 mod miller_rabin;
@@ -23,6 +24,7 @@ pub use self::fast_fourier_transform::{
     inverse_fast_fourier_transform,
 };
 pub use self::fast_power::fast_power;
+pub use self::gcd_of_n_numbers::gcd;
 pub use self::greatest_common_divisor::{
     greatest_common_divisor_iterative, greatest_common_divisor_recursive,
 };