Add collatz_sequence.rs (TheAlgorithms#402)

Author: Utshaan

src/math/collatz_sequence.rs

@@ -0,0 +1,32 @@
+// collatz conjecture : https://en.wikipedia.org/wiki/Collatz_conjecture
+pub fn sequence(mut n: usize) -> Option<Vec<usize>> {
+    if n == 0 {
+        return None;
+    }
+    let mut list: Vec<usize> = vec![];
+    while n != 1 {
+        list.push(n);
+        if n % 2 == 0 {
+            n /= 2;
+        } else {
+            n = 3 * n + 1;
+        }
+    }
+    list.push(n);
+    Some(list)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::sequence;
+
+    #[test]
+    fn validity_check() {
+        assert_eq!(sequence(10).unwrap(), [10, 5, 16, 8, 4, 2, 1]);
+        assert_eq!(
+            sequence(15).unwrap(),
+            [15, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1]
+        );
+        assert_eq!(sequence(0).unwrap_or_else(|| vec![0]), [0]);
+    }
+}

src/math/mod.rs

@@ -2,6 +2,7 @@ mod amicable_numbers;
 mod armstrong_number;
 mod baby_step_giant_step;
 mod chinese_remainder_theorem;
+mod collatz_sequence;
 mod doomsday;
 mod extended_euclidean_algorithm;
 mod fast_fourier_transform;
@@ -37,6 +38,7 @@ pub use self::amicable_numbers::amicable_pairs_under_n;
 pub use self::armstrong_number::is_armstrong_number;
 pub use self::baby_step_giant_step::baby_step_giant_step;
 pub use self::chinese_remainder_theorem::chinese_remainder_theorem;
+pub use self::collatz_sequence::sequence;
 pub use self::doomsday::get_week_day;
 pub use self::extended_euclidean_algorithm::extended_euclidean_algorithm;
 pub use self::fast_fourier_transform::{