I’ve been using Rust lately, and I really love it. I wrote a little binary search algorithm that’s generic over the container type, the index type, and the element type, and I thought I’d share it.

use std::cmp::Ordering; use std::ops::Add; use std::ops::Div; use std::ops::Index; use std::ops::Sub; pub trait BinarySearch<I, T> { /// Returns the index of an equal key, or the index at which the key would be inserted if one does not exist. fn binary_search(&self, key: &T, mut lower: I, mut upper: I) -> I; } // // Would use this, but std::num::One is unstable // impl <C, I, T> BinarySearch<I, T> for C // where // C: Index<I, Output = T>, // I: Ord + Add<Output = I> + Sub<Output = I> + Div<Output = I> + Shr<I, Output = I> + One + Copy, // T: Ord { // fn binary_search(&self, key: &T, mut lower: I, mut upper: I) -> I { // let one = I::one(); // loop { // if upper <= lower { // return lower; // } // let mid = (lower + upper).shr(one); // match key.cmp(&self[mid]) { // Ordering::Less => upper = mid, // Ordering::Greater => lower = mid + one, // Ordering::Equal => return mid, // } // } // } // } impl <C, I, T> BinarySearch<I, T> for C where C: Index<I, Output = T>, I: Ord + Add<Output = I> + Sub<Output = I> + Div<Output = I> + Shr<I, Output = I> + Copy, T: Ord { fn binary_search(&self, key: &T, mut lower: I, mut upper: I) -> I { if upper == lower { return lower; } let one = (upper - lower) / (upper - lower); loop { if upper <= lower { return lower; } let mid = (lower + upper).shr(one); match key.cmp(&self[mid]) { Ordering::Less => upper = mid, Ordering::Greater => lower = mid + one, Ordering::Equal => return mid, } } } } #[cfg(test)] mod tests { use super::*; #[test] fn test_binary_search() { let data = vec![0, 0, 1, 2, 4, 7]; for i in 0..data.len() { let ix = data.binary_search(&data[i], 0, data.len()); assert_eq!(data[ix], data[i]); // ix may not be i because of duplicates } assert_eq!(data.binary_search(&-1, 0, data.len()), 0); assert_eq!(data.binary_search(&3, 0, data.len()), 4); assert_eq!(data.binary_search(&5, 0, data.len()), 5); assert_eq!(data.binary_search(&8, 0, data.len()), 6); } }

Enjoy!

## One Comment

Appreciation to my father who told me about this

blog, this website is really awesome.

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