Add Dutch National Flag Sort (rust-lang#401)

Author: CenTdemeern1

src/sorting/dutch_national_flag_sort.rs

@@ -0,0 +1,65 @@
+/*
+A Rust implementation of the Dutch National Flag sorting algorithm.
+
+Reference implementation: https://github.com/TheAlgorithms/Python/blob/master/sorts/dutch_national_flag_sort.py
+More info: https://en.wikipedia.org/wiki/Dutch_national_flag_problem
+*/
+
+#[derive(PartialOrd, PartialEq, Eq)]
+pub enum Colors {
+    Red,   // \
+    White, //  | Define the three colors of the Dutch Flag: 🇳🇱
+    Blue,  // /
+}
+use Colors::*;
+
+// Algorithm implementation
+pub fn dutch_national_flag_sort(mut sequence: Vec<Colors>) -> Vec<Colors> {
+    // We take ownership of `sequence` because the original `sequence` will be modified and then returned
+    let length = sequence.len();
+    if length <= 1 {
+        return sequence; // Arrays of length 0 or 1 are automatically sorted
+    }
+    let mut low = 0;
+    let mut mid = 0;
+    let mut high = length - 1;
+    while mid <= high {
+        if sequence[mid] == Red {
+            sequence.swap(low, mid);
+            low += 1;
+            mid += 1;
+        } else if sequence[mid] == White {
+            mid += 1;
+        } else {
+            // Equivalent to `else if sequence[mid] == Blue`,
+            // because `Red`, `White`, and `Blue` are the only members of the Colors enum
+            sequence.swap(mid, high);
+            high -= 1;
+        }
+    }
+    sequence
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::is_sorted;
+    use super::*;
+
+    #[test]
+    fn random_array() {
+        let arr = vec![
+            Red, Blue, White, White, Blue, Blue, Red, Red, White, Blue, White, Red, White, Blue,
+        ];
+        let arr = dutch_national_flag_sort(arr);
+        assert!(is_sorted(&arr))
+    }
+
+    #[test]
+    fn sorted_array() {
+        let arr = vec![
+            Red, Red, Red, Red, Red, White, White, White, White, White, Blue, Blue, Blue, Blue,
+        ];
+        let arr = dutch_national_flag_sort(arr);
+        assert!(is_sorted(&arr))
+    }
+}

src/sorting/mod.rs

@@ -5,6 +5,7 @@ mod cocktail_shaker_sort;
 mod comb_sort;
 mod counting_sort;
 mod cycle_sort;
+mod dutch_national_flag_sort;
 mod exchange_sort;
 mod gnome_sort;
 mod heap_sort;
@@ -29,6 +30,7 @@ pub use self::comb_sort::comb_sort;
 pub use self::counting_sort::counting_sort;
 pub use self::counting_sort::generic_counting_sort;
 pub use self::cycle_sort::cycle_sort;
+pub use self::dutch_national_flag_sort::dutch_national_flag_sort;
 pub use self::exchange_sort::exchange_sort;
 pub use self::gnome_sort::gnome_sort;
 pub use self::heap_sort::heap_sort;