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!

## 3 Comments

This could be a fantastic buy if you are looking to mend a

toy hauler you already own. Many students of astral projection complain of dropping off to sleep while they perform the regular relaxation, meditation, and focusing

required of them. Europeans may prefer Cuba, while Americans who can’t check out Cuba may seek comfort and familiarity in Puerto Rico as well as the US Virgin Islands.

reproduced by hand, in contrast

By the end of the 15th century, 35