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//! [![Crates.io](https://img.shields.io/crates/v/shortlist.svg)](https://crates.io/crates/shortlist) //! [![Docs.rs](https://docs.rs/shortlist/badge.svg)](https://docs.rs/shortlist) //! //! A data structure to track the largest items pushed to it with no heap allocations and `O(1)` //! amortized time per push. //! //! # Features //! - Time complexity for pushing is `O(1)` amortized and `O(log n)` worst case (if the inputs are //! already sorted) //! - No heap allocations except when creating a new `Shortlist` //! - 0 dependencies, and only ~150 lines of source code //! - No `unsafe` //! //! # The Problem //! Suppose that you are running a brute force search over a very large search space, but want to //! keep more than just the single best item - for example, you want to find the best 100 items out //! of a search of a billion options. //! //! I.e. you want to implement the following function: //! ``` //! fn get_best<T: Ord>( //! big_computation: impl Iterator<Item = T>, //! n: usize //! ) -> Vec<T> { //! // Somehow get the `n` largest items produced by `big_computation` ... //! # vec![] //! } //! ``` //! //! # A bad solution //! The naive approach to this would be to store every item that we searched. Then once the search //! is complete, sort this list and then take however many items we need from the end of the list. //! This corresponds to roughly the following code: //! ``` //! fn get_best<T: Ord>( //! big_computation: impl Iterator<Item = T>, //! n: usize //! ) -> Vec<T> { //! // Collect all the results into a big sorted vec //! let mut giant_vec: Vec<T> = big_computation.collect(); //! giant_vec.sort(); //! // Return the last and therefore biggest n items with some iterator magic //! giant_vec.drain(..).rev().take(n).rev().collect() //! } //! //! # // Check that this does in fact do the right thing, albeit very slowly //! # assert_eq!( //! # get_best([0, 3, 2, 1, 4, 5].iter().copied(), 3), //! # vec![3, 4, 5] //! # ); //! ``` //! //! But this is massively inefficient in (at least) two ways: //! - Sorting very large lists is very slow, and we are sorting potentially billions of items that //! we will never need. //! - For any decently large search space, storing these items will likely crash the computer by //! making it run out of memory. //! //! # The solution used by this crate //! This is where using a `Shortlist` is useful. //! //! A `Shortlist` is a data structure that will dynamically keep a 'shortlist' of the best items //! given to it so far, with `O(1)` amortized time for pushing new items. It will also only perform //! one heap allocation when the `Shortlist` is created and every subsequent operation will be //! allocation free. Therefore, to the user of this library the code becomes: //! ``` //! use shortlist::Shortlist; //! //! fn get_best<T: Ord>( //! big_computation: impl Iterator<Item = T>, //! n: usize //! ) -> Vec<T> { //! // Create a new Shortlist that will take at most `n` items //! let mut shortlist = Shortlist::new(n); //! // Feed it all the results from `big_computation` //! for v in big_computation { //! shortlist.push(v); //! } //! // Return the shortlisted values as a sorted vec //! shortlist.into_sorted_vec() //! } //! //! # // Check that this does in fact do the right thing //! # assert_eq!( //! # get_best([0, 3, 2, 1, 4, 5].iter().copied(), 3), //! # vec![3, 4, 5] //! # ); //! ``` //! //! Or as a one-liner: //! ``` //! use shortlist::Shortlist; //! //! fn get_best<T: Ord>(big_computation: impl Iterator<Item = T>, n: usize) -> Vec<T> { //! Shortlist::from_iter(n, big_computation).into_sorted_vec() //! } //! //! # // Check that this does in fact do the right thing //! # assert_eq!( //! # get_best([0, 3, 2, 1, 4, 5].iter().copied(), 3), //! # vec![3, 4, 5] //! # ); //! ``` //! //! In both cases, the code will make exactly one heap allocation (to reserve space for the //! `Shortlist`). #![deny(clippy::cargo)] use std::cmp::Reverse; use std::collections::BinaryHeap; /// A data structure that tracks the largest items pushed to it with no heap allocations and `O(1)` /// amortized time per push. /// /// A `Shortlist` is a data structure that will dynamically keep a 'shortlist' of the best items /// given to it so far, with `O(1)` amortized time for pushing new items. It will also only perform /// one heap allocation when the `Shortlist` is created and every subsequent operation will be /// allocation free. /// /// # Example /// Find the top `100` values from 1000 randomly generated integers without storing more than 100 /// integers on the heap at a time. /// ``` /// use shortlist::Shortlist; /// use rand::prelude::*; /// /// // Make a Shortlist and tell it to allocate space for 100 usizes /// let mut shortlist: Shortlist<usize> = Shortlist::new(100); /// // Push 1000 random values between 0 and 10,000 /// let mut rng = thread_rng(); /// for _ in 0..1000 { /// shortlist.push(rng.gen_range(0, 10_000)); /// } /// // Consume the shortlist and print its top 100 items in ascending order /// println!("{:?}", shortlist.into_sorted_vec()); /// ``` #[derive(Debug, Clone)] pub struct Shortlist<T> { heap: BinaryHeap<Reverse<T>>, } impl<T: Ord> Shortlist<T> { /// Creates a new empty `Shortlist` with a given capacity. /// /// The capacity is the maximum number of items that the `Shortlist` will store at an any one /// time. /// Creating a new `Shortlist` causes one heap allocation, but will allocate enough memory /// to make sure that all subsequent operations cause no heap allocations. /// /// # Panics /// Creating a `Shortlist` with capacity `0` is a logical error and will cause a panic. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let shortlist: Shortlist<u64> = Shortlist::new(42); /// assert_eq!(shortlist.capacity(), 42); /// assert!(shortlist.is_empty()); /// ``` pub fn new(capacity: usize) -> Shortlist<T> { assert!(capacity > 0, "Cannot create a Shortlist with capacity 0."); Shortlist { heap: BinaryHeap::with_capacity(capacity), } } /// Creates a new `Shortlist` with a given capacity that contains [`Clone`]s of the largest /// items of a given slice. /// /// As with [`Shortlist::new`], this performs one heap allocation but every further operation /// on the `Shortlist` will not. /// /// If you want to `move` rather than `clone` the data, consider using [`Shortlist::from_iter`] /// instead. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let contents = [0, 3, 6, 5, 2, 1, 4, 6, 7]; /// let shortlist = Shortlist::from_slice(4, &contents); /// // The top 4 items of `contents` is [5, 6, 6, 7] /// assert_eq!(shortlist.into_sorted_vec(), vec![5, 6, 6, 7]); /// ``` pub fn from_slice(capacity: usize, contents: &[T]) -> Shortlist<T> where T: Clone, { let mut shortlist = Shortlist::new(capacity); shortlist.append_slice(contents); shortlist } /// Creates a new `Shortlist` with a given capacity that contains the largest items consumed /// from a given collection. /// /// As with [`Shortlist::new`], this performs one heap allocation but every further operation /// on the `Shortlist` will not. /// /// This does not [`Clone`] the items but instead consumes the [`Iterator`] by either moving /// all the values into the [`Shortlist`] or dropping them. /// If you would rather [`Clone`] the contents of the collection (so that the collection does /// not have to be consumed), consider using [`Shortlist::from_slice`] or using the /// [`cloned`](Iterator::cloned) iterator extension. /// /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let contents = [0, 3, 6, 5, 2, 1, 4, 6, 7]; /// let shortlist = Shortlist::from_iter(4, contents.iter().copied()); /// // The top 4 items of `contents` is [5, 6, 6, 7] /// assert_eq!(shortlist.into_vec(), vec![5, 6, 6, 7]); /// ``` pub fn from_iter(capacity: usize, contents: impl IntoIterator<Item = T>) -> Shortlist<T> { let mut shortlist = Shortlist::new(capacity); shortlist.append(contents); shortlist } /// Add an item to the `Shortlist`. /// /// Because capacity of a `Shortlist` is fixed, once this capacity is reached any new items /// will either be immediately dropped (if it is not large enough to make the shortlist) or the /// new item will cause an existing item in the `Shortlist` to be dropped. /// /// If the `item` is big enough and there are at least two minimum values, exactly which of /// these minimum items will be dropped is an implementation detail of the underlying /// [`BinaryHeap`] and cannot be relied upon. /// /// # Time Complexity /// The amortized cost of this operation, over all possible input sequence is `O(1)` (same as /// [`BinaryHeap::push`]). /// This degrades the more sorted the input sequence is. /// However, **unlike** [`BinaryHeap::push`] this will never reallocate, so the worst case cost of /// any single `push` is `O(log n)` where `n` is the length of the `Shortlist`. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// // Keep track of the 3 largest items so far. /// let mut shortlist = Shortlist::new(3); /// /// // The first two values will get added regardless of how small they are /// shortlist.push(0); /// shortlist.push(0); /// assert_eq!(shortlist.len(), 2); /// // Adding two more values will cause one of the 0s to get dropped from the Shortlist. /// // However, we don't know which `0` is still in the Shortlist /// shortlist.push(3); /// shortlist.push(4); /// // We now expect the shortlist to contain [0, 3, 4] /// assert_eq!(shortlist.into_sorted_vec(), vec![0, 3, 4]); /// ``` pub fn push(&mut self, item: T) { if self.heap.len() < self.heap.capacity() { // If the heap hasn't reached capacity we should always add the new item self.heap.push(Reverse(item)); } else { // If the heap is non-empty and `item` is less than this minimum we should early return // without modifying the shortlist if let Some(current_min) = self.heap.peek() { if item <= current_min.0 { return; } } // Since the heap is at capacity and `item` is bigger than the current table minimum, // we have to remove the minimum value to make space for `item` let popped = self.heap.pop(); debug_assert!(popped.is_some()); self.heap.push(Reverse(item)); } } /// Add an item to the `Shortlist` by reference, cloning it only if necessary. /// /// This is almost identical to [`Shortlist::push`], but gives better performance when cloning /// items since this will only [`Clone`] that item when it is added to the `Shortlist`. /// /// # Time Complexity /// Same as [`Shortlist::push`]. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// // Keep track of the 3 largest items so far. /// let mut shortlist: Shortlist<String> = Shortlist::new(3); /// /// // The first 3 strings will be added and therefore cloned /// shortlist.clone_push(&"Aardvark".to_string()); /// shortlist.clone_push(&"Zebra".to_string()); /// shortlist.clone_push(&"Manatee".to_string()); /// assert_eq!( /// shortlist.sorted_cloned_vec(), /// vec!["Aardvark".to_string(), "Manatee".to_string(), "Zebra".to_string()] /// ); /// // This will be cloned and added, causing "Aardvark" to be dropped /// shortlist.clone_push(&"Salamander".to_string()); /// assert_eq!( /// shortlist.sorted_cloned_vec(), /// vec!["Manatee".to_string(), "Salamander".to_string(), "Zebra".to_string()] /// ); /// // This won't be added but it also won't be cloned /// shortlist.clone_push(&"Elephant".to_string()); /// ``` pub fn clone_push(&mut self, item: &T) where T: Clone, { if self.heap.len() < self.heap.capacity() { // If the heap hasn't reached capacity we should always add the new item self.heap.push(Reverse(item.clone())); } else { // If the heap is non-empty and `item` is less than this minimum we should early return // without modifying the shortlist or cloning the item if let Some(current_min) = self.heap.peek() { if item <= ¤t_min.0 { return; } } // Since the heap is at capacity and `item` is bigger than the current table minimum, // we have to remove the minimum value to make space for `item` let popped = self.heap.pop(); debug_assert!(popped.is_some()); self.heap.push(Reverse(item.clone())); } } /// Returns the smallest value currently in this `Shortlist`. This can be used to check /// whether or not a new value will be permitted before spending time creating it. This /// operation takes constant time. pub fn peek_min(&self) -> Option<&T> { self.heap.peek().map(|x| &x.0) } /// Consume items from an iterator and add these to the `Shortlist`. /// /// This is equivalent to calling [`Shortlist::push`] on every item from `contents`. /// Similarly to [`Shortlist::from_iter`] this moves all the items rather than cloning them. /// If you would rather [`Clone`] the contents of the collection (so that the collection does /// not have to be consumed), consider using [`Shortlist::append_slice`] or using the /// [`cloned`](Iterator::cloned) iterator extension. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// // Keep track of the 3 biggest values seen so far /// let mut shortlist: Shortlist<usize> = Shortlist::new(3); /// // After adding [0, 4, 3, 2, 5], the 3 biggest values will be [3, 4, 5] /// shortlist.append([0, 4, 3, 2, 5].iter().copied()); /// assert_eq!(shortlist.sorted_cloned_vec(), vec![3, 4, 5]); /// // Most of these values are too small, but the 5 will cause the 3 to be /// // dropped from the Shortlist /// shortlist.append([0, 2, 2, 1, 5, 2].iter().copied()); /// assert_eq!(shortlist.sorted_cloned_vec(), vec![4, 5, 5]); /// ``` #[inline] pub fn append(&mut self, contents: impl IntoIterator<Item = T>) { for i in contents { self.push(i); } } /// Clone all items from a slice and add them to the `Shortlist`. /// /// This is equivalent to calling [`Shortlist::push`] on the [`Clone`] of every /// item in the slice. /// It will, however, be faster than using [`Shortlist::push`] because it internally uses /// [`Shortlist::clone_push`], which only clones the values if they are added to the /// `Shortlist`. /// If you want to move the items and consume the slice rather than cloning them, consider using /// [`Shortlist::append`] instead. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// // Keep track of the 3 biggest values seen so far /// let mut shortlist: Shortlist<usize> = Shortlist::new(3); /// // After adding [0, 4, 3, 2, 5], the 3 biggest values will be [3, 4, 5] /// shortlist.append_slice(&[0, 4, 3, 2, 5]); /// assert_eq!(shortlist.sorted_cloned_vec(), vec![3, 4, 5]); /// // Most of these values are too small, but the 5 will cause the 3 to be /// // dropped from the Shortlist /// shortlist.append_slice(&[0, 2, 2, 1, 5, 2]); /// assert_eq!(shortlist.sorted_cloned_vec(), vec![4, 5, 5]); /// ``` #[inline] pub fn append_slice(&mut self, contents: &[T]) where T: Clone, { for i in contents { self.clone_push(i); } } /// Consumes this `Shortlist` and return a [`Vec`] containing the contents of the `Shortlist` in /// ascending order. This code technically performs a heap allocation, but LLVM usually /// removes it when optimising. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let contents = [0, 3, 6, 5, 2, 1, 4, 6, 7]; /// let shortlist = Shortlist::from_slice(4, &contents); /// // The top 4 items of `contents` is [5, 6, 6, 7] /// assert_eq!(shortlist.into_sorted_vec(), vec![5, 6, 6, 7]); /// ``` pub fn into_sorted_vec(self) -> Vec<T> { let mut vec: Vec<T> = self .heap .into_vec() .into_iter() .map(|Reverse(v)| v) .collect(); vec.sort(); vec } /// Returns a [`Vec`] containing the [`Clone`]d contents of this `Shortlist` in ascending /// order, without the `Shortlist` being consumed. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let contents = [0, 3, 6, 5, 2, 1, 4, 6, 7]; /// let shortlist = Shortlist::from_slice(4, &contents); /// // The top 4 items of `contents` is [5, 6, 6, 7] /// assert_eq!(shortlist.sorted_cloned_vec(), vec![5, 6, 6, 7]); /// // Assert that the shortlist has not been consumed /// assert_eq!(shortlist.len(), 4); /// ``` pub fn sorted_cloned_vec(&self) -> Vec<T> where T: Clone, { let mut vec: Vec<T> = self.heap.iter().map(|Reverse(v)| v.clone()).collect(); vec.sort(); vec } } impl<T> Shortlist<T> { /// Returns an [`Iterator`] that borrows the items in a `Shortlist`, in an arbitrary order. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let contents = [0, 3, 6, 5, 2, 1, 4, 6, 7]; /// let mut shortlist = Shortlist::from_slice(3, &contents); /// // The top 3 items of `contents` is [6, 6, 7] /// let mut top_3: Vec<&usize> = shortlist.iter().collect(); /// top_3.sort(); /// assert_eq!(top_3, vec![&6, &6, &7]); /// // But we can still keep using the Shortlist /// shortlist.push(3); /// ``` #[inline] pub fn iter<'a>(&'a self) -> impl Iterator<Item = &'a T> + 'a { self.heap.iter().map(|x| &x.0) } /// Returns the maximum number of values that this `Shortlist` will store. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// // Make a new Shortlist with capacity 100 /// let shortlist: Shortlist<String> = Shortlist::new(100); /// assert_eq!(shortlist.capacity(), 100); /// ``` #[inline] pub fn capacity(&self) -> usize { self.heap.capacity() } /// Consumes this `Shortlist` and return a [`Vec`] containing the contents of the `Shortlist` /// in an arbitrary order. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let contents = [0, 3, 6, 5, 2, 1, 4, 6, 7]; /// let shortlist = Shortlist::from_slice(4, &contents); /// // The top 4 items of `contents` is [5, 6, 6, 7] /// let mut top_4 = shortlist.into_vec(); /// top_4.sort(); /// assert_eq!(top_4, vec![5, 6, 6, 7]); /// ``` pub fn into_vec(self) -> Vec<T> { self.heap .into_vec() .into_iter() .map(|Reverse(v)| v) .collect() } /// Returns the number of items in a `Shortlist`. /// /// This will never be greater than the [`capacity`](Shortlist::capacity). /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// // The shortlist starts with no items /// let mut shortlist = Shortlist::new(3); /// assert_eq!(shortlist.len(), 0); /// // The first 3 items will all get added, and so cause len to increase /// shortlist.push(4); /// assert_eq!(shortlist.len(), 1); /// shortlist.push(2); /// assert_eq!(shortlist.len(), 2); /// shortlist.push(5); /// assert_eq!(shortlist.len(), 3); /// // Adding a 4th item will cause an item to be dropped and the len to stay at 3 /// shortlist.push(6); /// assert_eq!(shortlist.len(), 3); /// ``` #[inline] pub fn len(&self) -> usize { self.heap.len() } /// Returns `true` if a `Shortlist` contains no items. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let mut shortlist = Shortlist::new(3); /// // The shortlist starts empty /// assert!(shortlist.is_empty()); /// // The shortlist is not empty if we push some values /// shortlist.push(4); /// assert!(!shortlist.is_empty()); /// shortlist.append_slice(&[0, 1, 2, 3]); /// assert!(!shortlist.is_empty()); /// // If we clear the shortlist, it becomes empty /// shortlist.clear(); /// assert!(shortlist.is_empty()); /// ``` #[inline] pub fn is_empty(&self) -> bool { self.heap.is_empty() } /// Returns an [`Iterator`] that pops the items from a `Shortlist` in an arbitrary order. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let mut shortlist = Shortlist::new(3); /// shortlist.append_slice(&[0, 1, 5, 2, 3, 5]); /// // Drain the shortlist into a vector, showing that the Shortlist is then empty /// let mut drained_values: Vec<usize> = shortlist.drain().collect(); /// assert!(shortlist.is_empty()); /// // Check that we drained the right values ([3, 5, 5]) /// drained_values.sort(); // The values are in arbitrary order /// assert_eq!(drained_values, vec![3, 5, 5]); /// ``` #[inline] pub fn drain<'a>(&'a mut self) -> impl Iterator<Item = T> + 'a { self.heap.drain().map(|Reverse(x)| x) } /// Remove and drop all the items in a `Shortlist`, leaving it empty. /// /// # Example /// ``` /// use shortlist::Shortlist; /// /// let mut shortlist = Shortlist::from_slice(3, &[0, 1, 2, 3]); /// // If we clear the shortlist, it becomes empty /// assert!(!shortlist.is_empty()); /// shortlist.clear(); /// assert!(shortlist.is_empty()); #[inline] pub fn clear(&mut self) { self.heap.clear(); } } #[cfg(test)] mod tests { use super::Shortlist; use rand::prelude::*; /* ===== HELPER FUNCTIONS ===== */ /// Given a sorted [`Vec`] of input values and a sorted [`Vec`] of the values taken from a /// [`Shortlist`] of those items, checks that the [`Shortlist`] behaved correctly. fn check_sorted_vecs<T: Ord + Eq + std::fmt::Debug>( sorted_input_values: Vec<T>, shortlist_vec: Vec<T>, capacity: usize, ) { let mut debug_lines = Vec::with_capacity(1000); debug_lines.push("".to_string()); debug_lines.push(format!("Input length : {}", sorted_input_values.len())); debug_lines.push(format!("Shortlist capacity: {}", capacity)); debug_lines.push(format!("Shortlist length : {}", shortlist_vec.len())); // let shortlist_vec = shortlist.into_sorted_vec(); // Check that the shortlist's length is the minimum of its capacity and the number of input // values if shortlist_vec.len() != capacity.min(sorted_input_values.len()) { debug_lines.push(format!("Input values: {:?}", sorted_input_values)); debug_lines.push(format!("Shortlisted values: {:?}", shortlist_vec)); // Print the debug info before panicking for line in debug_lines { println!("{}", line); } panic!(); } // Check that `shortlist.into_sorted_vec()` produces a suffix of `input_values` (we can // guaruntee that the input values are sorted). for (val, exp_val) in shortlist_vec .iter() .rev() .zip(sorted_input_values.iter().rev()) { if val == exp_val { debug_lines.push(format!("{:?} == {:?}", val, exp_val)); } else { debug_lines.push(format!("{:?} != {:?}", val, exp_val)); // Print the debug info before panicking for line in debug_lines { println!("{}", line); } panic!(); } } } /// Generates a random capacity and randomised input [`Vec`] to be used as a test sample. fn gen_sample_input(rng: &mut impl Rng) -> (usize, Vec<usize>) { // Decide how much capacity the shortlist will have let capacity = rng.gen_range(1, 100); // Make empty collections let mut input_values: Vec<usize> = Vec::new(); // Populate both collections with the same values for _ in 0..rng.gen_range(1, 1000) { let val = rng.gen_range(0, 1000); input_values.push(val); } (capacity, input_values) } /// Generates a randomised chunk of input data and a [`Shortlist`] built from that data. The /// [`Vec`] returned is always sorted, though the [`Shortlist`] is generated from the unsorted /// data to be a fair test. fn generate_input_and_shortlist(rng: &mut impl Rng) -> (Vec<usize>, Shortlist<usize>) { let (capacity, mut input_values) = gen_sample_input(rng); let shortlist: Shortlist<usize> = Shortlist::from_slice(capacity, &input_values); // Sort the input values and return input_values.sort(); (input_values, shortlist) } /// Test a given check over [`Shortlist`]s many times. fn check_correctness(check: impl Fn(Vec<usize>, Shortlist<usize>) -> ()) { let mut rng = thread_rng(); // Make a shortlist with a known set of values for _ in 1..10_000 { let (input_values, shortlist) = generate_input_and_shortlist(&mut rng); // Check that the shortlist contains a suffix of the sorted reference vec check(input_values, shortlist); } } /* ===== TESTING FUNCTIONS ===== */ #[test] fn iter() { check_correctness(|values, shortlist| { // Store the capacity for both tests to use let capacity = shortlist.capacity(); // Unload the Shortlist using `Shortlist::iter` let mut shortlist_vec: Vec<usize> = shortlist.iter().copied().collect(); shortlist_vec.sort(); check_sorted_vecs(values, shortlist_vec, capacity); }); } #[test] fn into_sorted_vec() { check_correctness(|values, shortlist| { let capacity = shortlist.capacity(); let shortlist_vec = shortlist.into_sorted_vec(); check_sorted_vecs(values, shortlist_vec, capacity); }); } #[test] fn sorted_cloned_vec() { check_correctness(|values, shortlist| { let capacity = shortlist.capacity(); let shortlist_vec = shortlist.sorted_cloned_vec(); check_sorted_vecs(values, shortlist_vec, capacity); // Check that the shortlist still has its values }); } #[test] fn into_vec() { check_correctness(|values, shortlist| { let capacity = shortlist.capacity(); let mut shortlist_vec = shortlist.into_vec(); shortlist_vec.sort(); check_sorted_vecs(values, shortlist_vec, capacity); }); } #[test] fn drain() { check_correctness(|values, mut shortlist| { let capacity = shortlist.capacity(); let mut shortlist_vec: Vec<usize> = shortlist.drain().collect(); // If we have drained the shortlist, it must be empty assert!(shortlist.is_empty()); // Test that drain returned the right values shortlist_vec.sort(); check_sorted_vecs(values, shortlist_vec, capacity); }); } #[test] fn clear() { check_correctness(|_values, mut shortlist| { // Clear the shortlist and assert that it is now empty shortlist.clear(); assert!(shortlist.is_empty()); }); } #[test] fn append() { let mut rng = thread_rng(); // Make a shortlist with a known set of values for _ in 1..10_000 { let (capacity, mut input_values) = gen_sample_input(&mut rng); let shortlist: Shortlist<usize> = Shortlist::from_iter(capacity, input_values.iter().copied()); // Sort the input values input_values.sort(); // Check that the shortlist contains a suffix of the sorted reference vec let mut shortlist_vec = shortlist.into_vec(); shortlist_vec.sort(); check_sorted_vecs(input_values, shortlist_vec, capacity); } } /// Tests [`Shortlist::len`], [`Shortlist::capacity`], [`Shortlist::is_empty`] #[test] fn capacity_and_len() { let mut rng = thread_rng(); // Make a shortlist with a known set of values for _ in 1..10_000 { // Generate a test sample let (capacity, mut input_values) = gen_sample_input(&mut rng); // Add the values to the shortlist, asserting that the length and capacity are always // correct let mut shortlist: Shortlist<usize> = Shortlist::new(capacity); for (i, val) in input_values.iter().copied().enumerate() { // The length of the shortlist should increase every time we add an element, unless // the shortlist is full in which case it will stay at the capacity forever assert_eq!(shortlist.len(), i.min(capacity)); // The capacity of the shortlist should never change assert_eq!(shortlist.capacity(), capacity); // Add the new value shortlist.push(val); // If we have pushed any values, the shortlist cannot be empty assert!(!shortlist.is_empty()); } // Sort the input values input_values.sort(); // Check that the shortlist contains a suffix of the sorted reference vec let mut shortlist_vec = shortlist.into_vec(); shortlist_vec.sort(); check_sorted_vecs(input_values, shortlist_vec, capacity); } } }