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

1. use std::cmp::PartialEq;

3. pub fn linear_search<T: PartialEq>(item: &T, arr: &[T]) -> Option<usize> {
4. for (i, data) in arr.iter().enumerate() {
5. if item == data {
6. return Some(i);
7. }
8. }

10. None
11. }

13. #[cfg(test)]
14. mod tests {
15. use super::*;

17. #[test]
18. fn search_strings() {
19. let index = linear_search(&"a", &vec!["a", "b", "c", "d", "google", "zoo"]);
20. assert_eq!(index, Some(0));
21. }

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

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

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

34. let index = linear_search(&1, &vec![1, 2, 3, 4]);
35. assert_eq!(index, Some(0));
36. }

38. #[test]
39. fn not_found() {
40. let index = linear_search(&5, &vec![1, 2, 3, 4]);
41. assert_eq!(index, None);
42. }

44. #[test]
45. fn empty() {
46. let index = linear_search(&1, &vec![]);
47. assert_eq!(index, None);
48. }
49. }