mirror of
https://github.com/mfocko/blog.git
synced 2024-11-22 04:53:47 +01:00
blog(aoc-2022): mention min-heap in 4th week
Signed-off-by: Matej Focko <me@mfocko.xyz>
This commit is contained in:
parent
47c4168dff
commit
6431d4325b
1 changed files with 45 additions and 0 deletions
|
@ -450,6 +450,48 @@ let next_positions = |p| {
|
|||
};
|
||||
```
|
||||
|
||||
#### Min-heap
|
||||
|
||||
In this case I had a need to use the priority queue taking the elements with the
|
||||
lowest cost as the prioritized ones. Rust only offers you the [`BinaryHeap`] and
|
||||
that is a max-heap. One of the ways how to achieve a min-heap is to put the
|
||||
elements in wrapped in a [`Reverse`] (as is even showed in the linked [docs of
|
||||
the `BinaryHeap`]). However the wrapping affects the type of the heap and also
|
||||
popping the most prioritized elements yields values wrapped in the `Reverse`.
|
||||
|
||||
For this purpose I have just taken the max-heap and wrapped it as a whole in a
|
||||
separate structure providing just the desired methods:
|
||||
```rust
|
||||
use std::cmp::{Ord, Reverse};
|
||||
use std::collections::BinaryHeap;
|
||||
|
||||
pub struct MinHeap<T> {
|
||||
heap: BinaryHeap<Reverse<T>>,
|
||||
}
|
||||
|
||||
impl<T: Ord> MinHeap<T> {
|
||||
pub fn new() -> MinHeap<T> {
|
||||
MinHeap {
|
||||
heap: BinaryHeap::new(),
|
||||
}
|
||||
}
|
||||
|
||||
pub fn push(&mut self, item: T) {
|
||||
self.heap.push(Reverse(item))
|
||||
}
|
||||
|
||||
pub fn pop(&mut self) -> Option<T> {
|
||||
self.heap.pop().map(|Reverse(x)| x)
|
||||
}
|
||||
}
|
||||
|
||||
impl<T: Ord> Default for MinHeap<T> {
|
||||
fn default() -> Self {
|
||||
Self::new()
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
Rest is just the algorithm implementation which is not that interesting.
|
||||
|
||||
## [Day 25: Full of Hot Air](https://adventofcode.com/2022/day/25)
|
||||
|
@ -592,3 +634,6 @@ See you next year! Maybe in Rust, maybe not :upside_down_face:
|
|||
|
||||
[_Advent of Code_]: https://adventofcode.com
|
||||
[_A\*_]: https://en.wikipedia.org/wiki/A*_search_algorithm
|
||||
[`BinaryHeap`]: https://doc.rust-lang.org/std/collections/struct.BinaryHeap.html
|
||||
[`Reverse`]: https://doc.rust-lang.org/std/cmp/struct.Reverse.html
|
||||
[docs of the `BinaryHeap`]: https://doc.rust-lang.org/std/collections/struct.BinaryHeap.html#min-heap
|
||||
|
|
Loading…
Reference in a new issue