fix: bubble_sort failed when vec is empty (rust-lang#348)

Author: Yaxian

src/sorting/bubble_sort.rs

@@ -1,4 +1,7 @@
 pub fn bubble_sort<T: Ord>(arr: &mut [T]) {
+    if arr.is_empty() {
+        return;
+    }
     let mut sorted = false;
     let mut n = arr.len();
     while !sorted {
@@ -15,25 +18,28 @@ pub fn bubble_sort<T: Ord>(arr: &mut [T]) {
 
 #[cfg(test)]
 mod tests {
+    use super::super::is_sorted;
     use super::*;
 
     #[test]
     fn descending() {
         //descending
         let mut ve1 = vec![6, 5, 4, 3, 2, 1];
         bubble_sort(&mut ve1);
-        for i in 0..ve1.len() - 1 {
-            assert!(ve1[i] <= ve1[i + 1]);
-        }
+        assert!(is_sorted(&ve1));
     }
 
     #[test]
     fn ascending() {
         //pre-sorted
         let mut ve2 = vec![1, 2, 3, 4, 5, 6];
         bubble_sort(&mut ve2);
-        for i in 0..ve2.len() - 1 {
-            assert!(ve2[i] <= ve2[i + 1]);
-        }
+        assert!(is_sorted(&ve2));
+    }
+    #[test]
+    fn empty() {
+        let mut ve3: Vec<usize> = vec![];
+        bubble_sort(&mut ve3);
+        assert!(is_sorted(&ve3));
     }
 }