fix: empty slice panics in bead_sort, bogo_sort, comb_sort and wave_sort

src/sorting/bead_sort.rs

@@ -1,6 +1,11 @@
 //Bead sort only works for sequences of non-negative integers.
 //https://en.wikipedia.org/wiki/Bead_sort
 pub fn bead_sort(a: &mut [usize]) {
+    // An empty slice has no maximum to seed the bead grid with.
+    if a.is_empty() {
+        return;
+    }
+
     // Find the maximum element
     let mut max = a[0];
     (1..a.len()).for_each(|i| {
@@ -56,4 +61,28 @@ mod tests {
         bead_sort(&mut ve2);
         assert!(is_sorted(&ve2) && have_same_elements(&ve2, &cloned));
     }
+
+    #[test]
+    fn empty() {
+        let mut ve3: Vec<usize> = vec![];
+        let cloned = ve3.clone();
+        bead_sort(&mut ve3);
+        assert!(is_sorted(&ve3) && have_same_elements(&ve3, &cloned));
+    }
+
+    #[test]
+    fn one_element() {
+        let mut ve4: [usize; 1] = [4];
+        let cloned = ve4;
+        bead_sort(&mut ve4);
+        assert!(is_sorted(&ve4) && have_same_elements(&ve4, &cloned));
+    }
+
+    #[test]
+    fn all_zeroes() {
+        let mut ve5: [usize; 3] = [0, 0, 0];
+        let cloned = ve5;
+        bead_sort(&mut ve5);
+        assert!(is_sorted(&ve5) && have_same_elements(&ve5, &cloned));
+    }
 }

src/sorting/bogo_sort.rs

@@ -4,13 +4,8 @@ use std::time::{SystemTime, UNIX_EPOCH};
 const DEFAULT: u64 = 4294967296;
 
 fn is_sorted<T: Ord>(arr: &[T], len: usize) -> bool {
-    for i in 0..len - 1 {
-        if arr[i] > arr[i + 1] {
-            return false;
-        }
-    }
-
-    true
+    // `windows` yields nothing below two elements, where `0..len - 1` underflowed.
+    arr[..len].windows(2).all(|pair| pair[0] <= pair[1])
 }
 
 #[cfg(target_pointer_width = "64")]
@@ -70,4 +65,18 @@ mod tests {
             assert!(arr[i] <= arr[i + 1]);
         }
     }
+
+    #[test]
+    fn empty() {
+        let mut arr: Vec<i32> = vec![];
+        bogo_sort(&mut arr);
+        assert!(arr.is_empty());
+    }
+
+    #[test]
+    fn one_element() {
+        let mut arr = [7];
+        bogo_sort(&mut arr);
+        assert_eq!(&arr, &[7]);
+    }
 }

src/sorting/comb_sort.rs

@@ -1,4 +1,10 @@
 pub fn comb_sort<T: Ord>(arr: &mut [T]) {
+    // `gap` is clamped to at least 1 below, so `arr.len() - gap` would underflow
+    // on an empty slice.
+    if arr.len() < 2 {
+        return;
+    }
+
     let mut gap = arr.len();
     let shrink = 1.3;
     let mut sorted = false;
@@ -51,4 +57,20 @@ mod tests {
         comb_sort(&mut ve3);
         assert!(is_sorted(&ve3) && have_same_elements(&ve3, &cloned));
     }
+
+    #[test]
+    fn empty() {
+        let mut ve4: Vec<u8> = vec![];
+        let cloned = ve4.clone();
+        comb_sort(&mut ve4);
+        assert!(is_sorted(&ve4) && have_same_elements(&ve4, &cloned));
+    }
+
+    #[test]
+    fn one_element() {
+        let mut ve5 = vec![3];
+        let cloned = ve5.clone();
+        comb_sort(&mut ve5);
+        assert!(is_sorted(&ve5) && have_same_elements(&ve5, &cloned));
+    }
 }

src/sorting/wave_sort.rs

@@ -19,7 +19,8 @@ pub fn wave_sort<T: Ord>(arr: &mut [T]) {
     let n = arr.len();
     arr.sort();
 
-    for i in (0..n - 1).step_by(2) {
+    // `saturating_sub` keeps an empty slice from underflowing to `usize::MAX`.
+    for i in (0..n.saturating_sub(1)).step_by(2) {
         arr.swap(i, i + 1);
     }
 }
@@ -67,4 +68,18 @@ mod tests {
         let expected = vec![10, 5, 20, 15, 25];
         assert_eq!(&array, &expected);
     }
+
+    #[test]
+    fn empty() {
+        let mut array: Vec<i32> = vec![];
+        wave_sort(&mut array);
+        assert!(array.is_empty());
+    }
+
+    #[test]
+    fn one_element() {
+        let mut array = vec![42];
+        wave_sort(&mut array);
+        assert_eq!(&array, &[42]);
+    }
 }