线性搜索

From Wikipedia: linear search or sequential search is a method for finding a target value within a list. It sequentially checks each element of the list for the target value until a match is found or until all the elements have been searched. Linear search runs in at worst linear time and makes at most n comparisons, where n is the length of the list.

Properties

• Worst case performance O(n)
• Best case performance O(1)
• Average case performance O(n)
• Worst case space complexity O(1) iterative

#![allow(unused)]
fn main() {
use std::cmp::PartialEq;

pub fn linear_search<T: PartialEq>(item: &T, arr: &[T]) -> Option<usize> {
    for (i, data) in arr.iter().enumerate() {
        if item == data {
            return Some(i);
        }
    }

    None
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn search_strings() {
        let index = linear_search(&"a", &vec!["a", "b", "c", "d", "google", "zoo"]);
        assert_eq!(index, Some(0));
    }

    #[test]
    fn search_ints() {
        let index = linear_search(&4, &vec![1, 2, 3, 4]);
        assert_eq!(index, Some(3));

        let index = linear_search(&3, &vec![1, 2, 3, 4]);
        assert_eq!(index, Some(2));

        let index = linear_search(&2, &vec![1, 2, 3, 4]);
        assert_eq!(index, Some(1));

        let index = linear_search(&1, &vec![1, 2, 3, 4]);
        assert_eq!(index, Some(0));
    }

    #[test]
    fn not_found() {
        let index = linear_search(&5, &vec![1, 2, 3, 4]);
        assert_eq!(index, None);
    }

    #[test]
    fn empty() {
        let index = linear_search(&1, &vec![]);
        assert_eq!(index, None);
    }
}
}