Regarding bubble sort & sort api

help
1

Hi folks, wish you're doing fine!

Could anyone help explain the sort() api for slice from the std lib a bit more to me... because I'm not sure whether I should use it in sorting algorithms implementations..

Taking the bubble_sort() implementation as an example, it seems that I could NEVER pass the test without this sort() api @ln2, but don't know why it should be like that?

And also wondering why still have to implement sorting algorithm when this std api can already sort slice in asc order in the 1st place?)

Here is my code (pls kindly refer):slight_smile:
They both seem to stop at the end of single pass (without moving to next loop, which is weird..)

fn bubble_sort<T>(arr: &mut [T]) -> &[T] where T: Ord + PartialEq + Eq  {
    // arr.sort(); // I need to activate this to pass the test
    for i in 0..arr.len() - 1 {
        if arr[i] > arr[i + 1] { 
            arr.swap(i, i + 1);
        }
    }
    arr
} 

mod test {
    use super::*;

    #[test]
    fn shoud_work1() {
        let mut vec = [1, 2, 5, 4, 3];
        let res = bubble_sort(&mut vec);
        assert_eq!(res, &[1, 2, 3, 4, 5]);
    }
    #[test]
    fn shoud_work2() {
        let mut vec = [5, 4, 3, 2, 1];
        let res = bubble_sort(&mut vec);
        assert_eq!(res, &[1, 2, 3, 4, 5]);
    }

thread 'test::shoud_work1' (47) panicked at src/lib.rs:73:9:
assertion `left == right` failed
  left: [1, 2, 4, 3, 5]
 right: [1, 2, 3, 4, 5]

---- test::shoud_work2 stdout ----

thread 'test::shoud_work2' (48) panicked at src/lib.rs:79:9:
assertion `left == right` failed
  left: [4, 3, 2, 1, 5]
 right: [1, 2, 3, 4, 5]
2

please put all of your code snippets into rust code block, as explained in the top pinned post of theis forum, including your bubble_sort and your tests.

your implementation of bubble_sort is simply incorrect, and thus you are failing the tests.
calling sort correctly sorts the input, and your implementation luckily does nothing the input is already sorted.

bubble_sort requires a double loop, but you only have a simple loop.

3

The for-loop is not enough - you need another loop around it - keep looping until there are no swaps in the for-loop...

4

Got it! just add [for _ in 0..arr.len() - 1], it works & Thank you so much!

5

sort and friends each perform some sorting algorithm. Some methods have additional guarantees like being “stable”, meaning that the order of equal elements is preserved.

Each method’s implementation is chosen to be fast in a variety of situations. Their current implementations are documented, but the implementations are not guaranteed to remain the same, so that they can be changed if a different algorithm is found to be better.

If you’re implementing sorting algorithms for schoolwork or to compare the performance of different sorting algorithms, then don’t use this API. If you’re just trying to sort a slice, then I’d recommend that you use one of the sort methods and not implement a sorting algorithm.

Not sure why you “have to”, but see my above paragraph.