计数排序

1. /// In place counting sort for collections of u32
2. /// O(n + maxval) in time, where maxval is the biggest value an input can possibly take
3. /// O(maxval) in memory
4. /// u32 is chosen arbitrarly, a counting sort probably should'nt be used on data that requires bigger types.

6. pub fn counting_sort(arr: &mut [u32], maxval: usize) {
7. let mut occurences: Vec<usize> = vec![0; maxval + 1];

9. for &data in arr.iter() {
10. occurences[data as usize] += 1;
11. }

13. let mut i = 0;
14. for (data, &number) in occurences.iter().enumerate() {
15. for _ in 0..number {
16. arr[i] = data as u32;
17. i += 1;
18. }
19. }
20. }

22. use std::ops::AddAssign;
23. /// Generic implementation of a counting sort for all usigned types
24. pub fn generic_counting_sort<T: Into<u64> + From<u8> + AddAssign + Copy>(
25. arr: &mut [T],
26. maxval: usize,
27. ) {
28. let mut occurences: Vec<usize> = vec![0; maxval + 1];

30. for &data in arr.iter() {
31. occurences[data.into() as usize] += 1;
32. }

34. // Current index in output array
35. let mut i = 0;

37. // current data point, necessary to be type-safe
38. let mut data = T::from(0);

40. // This will iterate from 0 to the largest data point in `arr`
41. // `number` contains the occurances of the data point `data`
42. for &number in occurences.iter() {
43. for _ in 0..number {
44. arr[i] = data;
45. i += 1;
46. }

48. data += T::from(1);
49. }
50. }

52. #[cfg(test)]
53. mod test {
54. use super::super::is_sorted;
55. use super::*;

57. #[test]
58. fn counting_sort_descending() {
59. let mut ve1 = vec![6, 5, 4, 3, 2, 1];
60. counting_sort(&mut ve1, 6);

62. assert!(is_sorted(&ve1));
63. }

65. #[test]
66. fn counting_sort_pre_sorted() {
67. let mut ve2 = vec![1, 2, 3, 4, 5, 6];
68. counting_sort(&mut ve2, 6);

70. assert!(is_sorted(&ve2));
71. }

73. #[test]
74. fn generic_counting_sort() {
75. let mut ve1: Vec<u8> = vec![100, 30, 60, 10, 20, 120, 1];
76. super::generic_counting_sort(&mut ve1, 120);

78. assert!(is_sorted(&ve1));
79. }

81. #[test]
82. fn presorted_u64_counting_sort() {
83. let mut ve2: Vec<u64> = vec![1, 2, 3, 4, 5, 6];
84. super::generic_counting_sort(&mut ve2, 6);

86. assert!(is_sorted(&ve2));
87. }
88. }