Add stooge sort (rust-lang#224)

Author: jerr-it

DIRECTORY.md

@@ -50,6 +50,7 @@
     * [Radix Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/radix_sort.rs)
     * [Selection Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/selection_sort.rs)
     * [Shell Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/shell_sort.rs)
+    * [Stooge Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/stooge_sort.rs)
   * String
     * [Knuth Morris Pratt](https://github.com/TheAlgorithms/Rust/blob/master/src/string/knuth_morris_pratt.rs)
     * [Manacher](https://github.com/TheAlgorithms/Rust/blob/master/src/string/manacher.rs)

README.md

@@ -17,6 +17,7 @@ RESTART BUILD
 - [x] [Radix](./src/sorting/radix_sort.rs)
 - [x] [Selection](./src/sorting/selection_sort.rs)
 - [x] [Shell](./src/sorting/shell_sort.rs)
+- [x] [Stooge](./src/sorting/stooge_sort.rs)
 
 ## Graphs
 

src/sorting/README.md

@@ -100,6 +100,14 @@ __Properties__
 
 ###### View the algorithm in [action][shell-toptal]
 
+### [Stooge](./stooge_sort.rs)
+![alt text][stooge-image]
+
+From [Wikipedia][stooge-wiki]:  Stooge sort is a recursive sorting algorithm. It is notable for its exceptionally bad time complexity of O(n^(log 3 / log 1.5)) = O(n^2.7095...). The running time of the algorithm is thus slower compared to reasonable sorting algorithms, and is slower than Bubble sort, a canonical example of a fairly inefficient sort. It is however more efficient than Slowsort. The name comes from The Three Stooges.
+
+__Properties__
+* Worst case performance O(n^(log(3) / log(1.5)))
+
 [bubble-toptal]: https://www.toptal.com/developers/sorting-algorithms/bubble-sort
 [bubble-wiki]: https://en.wikipedia.org/wiki/Bubble_sort
 [bubble-image]: https://upload.wikimedia.org/wikipedia/commons/thumb/8/83/Bubblesort-edited-color.svg/220px-Bubblesort-edited-color.svg.png "Bubble Sort"
@@ -128,3 +136,6 @@ __Properties__
 [shell-toptal]: https://www.toptal.com/developers/sorting-algorithms/shell-sort
 [shell-wiki]: https://en.wikipedia.org/wiki/Shellsort
 [shell-image]: https://upload.wikimedia.org/wikipedia/commons/d/d8/Sorting_shellsort_anim.gif "Shell Sort"
+
+[stooge-image]: https://upload.wikimedia.org/wikipedia/commons/f/f8/Sorting_stoogesort_anim.gif
+[stooge-wiki]: https://en.wikipedia.org/wiki/Stooge_sort

src/sorting/mod.rs

@@ -7,6 +7,7 @@ mod quick_sort;
 mod radix_sort;
 mod selection_sort;
 mod shell_sort;
+mod stooge_sort;
 
 pub use self::bubble_sort::bubble_sort;
 pub use self::counting_sort::counting_sort;
@@ -18,6 +19,7 @@ pub use self::quick_sort::quick_sort;
 pub use self::radix_sort::radix_sort;
 pub use self::selection_sort::selection_sort;
 pub use self::shell_sort::shell_sort;
+pub use self::stooge_sort::stooge_sort;
 
 use std::cmp;
 

src/sorting/stooge_sort.rs

@@ -0,0 +1,63 @@
+fn _stooge_sort<T: Ord>(arr: &mut [T], start: usize, end: usize) {
+    if arr[start] > arr[end] {
+        arr.swap(start, end);
+    }
+
+    if start + 1 >= end {
+        return;
+    }
+
+    let k = (end - start + 1) / 3;
+
+    _stooge_sort(arr, start, end - k);
+    _stooge_sort(arr, start + k, end);
+    _stooge_sort(arr, start, end - k);
+}
+
+pub fn stooge_sort<T: Ord>(arr: &mut [T]) {
+    let len = arr.len();
+    if len == 0 {
+        return;
+    }
+
+    _stooge_sort(arr, 0, len - 1);
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn basic() {
+        let mut vec = vec![3, 5, 6, 3, 1, 4];
+        stooge_sort(&mut vec);
+        for i in 0..vec.len() - 1 {
+            assert!(vec[i] <= vec[i + 1]);
+        }
+    }
+
+    #[test]
+    fn empty() {
+        let mut vec: Vec<i32> = vec![];
+        stooge_sort(&mut vec);
+        assert_eq!(vec, vec![]);
+    }
+
+    #[test]
+    fn reverse() {
+        let mut vec = vec![6, 5, 4, 3, 2, 1];
+        stooge_sort(&mut vec);
+        for i in 0..vec.len() - 1 {
+            assert!(vec[i] <= vec[i + 1]);
+        }
+    }
+
+    #[test]
+    fn already_sorted() {
+        let mut vec = vec![1, 2, 3, 4, 5, 6];
+        stooge_sort(&mut vec);
+        for i in 0..vec.len() - 1 {
+            assert!(vec[i] <= vec[i + 1]);
+        }
+    }
+}