294 lines
7.0 KiB
Go
294 lines
7.0 KiB
Go
package stream
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import (
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"math"
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"runtime"
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)
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/**
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* Reference:
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* http://www.cnblogs.com/gw811/archive/2012/10/04/2711746.html
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*/
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// Comparator 比较器
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type Comparator struct {
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CompareTo func(interface{}, interface{}) int
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}
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// Sorted 对数据流操作，升序排序
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func (s *Stream) Sorted(comparator *Comparator) *Stream {
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return s.MSorted(comparator)
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}
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// QSorted 对数据流操作，快排，升序排序
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func (s *Stream) QSorted(comparator *Comparator) *Stream {
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qsort(s.list, 0, len(s.list), comparator.CompareTo)
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s.isParallel = false
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return s
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}
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// MSorted 对数据流操作，归并排序，升序排序
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func (s *Stream) MSorted(comparator *Comparator) *Stream {
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aux := make([]interface{}, len(s.list)) //辅助切片
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var ch chan int
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cores := runtime.NumCPU()
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maxDepth := int(math.Log2(float64(cores)) + 1)
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if s.isParallel {
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ch = make(chan int)
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for j := 0; j < cores; j++ {
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go func(idx int) {
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for i := idx; i < len(s.list); i += cores {
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aux[i] = s.list[i]
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}
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ch <- 0
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}(j)
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}
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waitCh(ch, cores)
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go mergeSort(aux, s.list, 0, len(s.list), 0, comparator.CompareTo, 0, maxDepth, ch)
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waitCh(ch, 1)
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} else {
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for i, v := range s.list {
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aux[i] = v
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}
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mergeSort(aux, s.list, 0, len(s.list), 0, comparator.CompareTo, 0, maxDepth, ch)
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}
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s.isParallel = false
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return s
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}
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func waitCh(ch chan int, num int) {
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if ch != nil {
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for i := 0; i < num; i++ {
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<-ch
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}
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}
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}
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/**
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* 对指定 int 型数组的指定范围按数字升序进行排序。
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*/
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func qsort(list []interface{}, fromIndex int, toIndex int, comp func(interface{}, interface{}) int) {
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qsort1(list, fromIndex, toIndex-fromIndex, comp)
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}
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func qsort1(list []interface{}, off int, len int, comp func(interface{}, interface{}) int) {
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/*
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* 当待排序的数组中的元素个数小于 7 时，采用插入排序 。
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*
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* 尽管插入排序的时间复杂度为O(n^2),但是当数组元素较少时， 插入排序优于快速排序，因为这时快速排序的递归操作影响性能。
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*/
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if len < 7 {
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for i := off; i < len+off; i++ {
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for j := i; j > off && comp(list[j-1], list[j]) > 0; j-- {
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swap(list, j, j-1)
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}
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}
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return
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}
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/*
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* 当待排序的数组中的元素个数大于 或等于7 时，采用快速排序 。
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*
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* Choose a partition element, v
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* 选取一个划分元，V
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*
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* 较好的选择了划分元(基准元素)。能够将数组分成大致两个相等的部分，避免出现最坏的情况。例如当数组有序的的情况下，
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* 选择第一个元素作为划分元，将使得算法的时间复杂度达到O(n^2).
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*/
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// 当数组大小为size=7时 ，取数组中间元素作为划分元。
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m := off + (len >> 1)
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// 当数组大小 7<size<=40时，取首、中、末 三个元素中间大小的元素作为划分元。
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if len > 7 {
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l := off
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n := off + len - 1
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/*
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* 当数组大小 size>40 时 ，从待排数组中较均匀的选择9个元素，
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* 选出一个伪中数做为划分元。
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*/
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if len > 40 {
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s := len / 8
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l = med3(list, l, l+s, l+2*s, comp)
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m = med3(list, m-s, m, m+s, comp)
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n = med3(list, n-2*s, n-s, n, comp)
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}
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// 取出中间大小的元素的位置。
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m = med3(list, l, m, n, comp) // Mid-size, med of 3
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}
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//得到划分元V
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v := list[m]
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// Establish Invariant: v* (<v)* (>v)* v*
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a := off
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b := a
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c := off + len - 1
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d := c
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for true {
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for b <= c && comp(list[b], v) <= 0 {
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if list[b] == v {
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swap(list, a, b)
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a++
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}
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b++
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}
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for c >= b && comp(list[c], v) >= 0 {
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if comp(list[c], v) == 0 {
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swap(list, c, d)
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d--
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}
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c--
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}
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if b > c {
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break
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}
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swap(list, b, c)
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b++
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c--
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}
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// Swap partition elements back to middle
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s := off + len
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n := s
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s = min(a-off, b-a)
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vecswap(list, off, b-s, s)
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s = min(d-c, n-d-1)
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vecswap(list, b, n-s, s)
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// Recursively sort non-partition-elements
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s = b - a
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if s > 1 {
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qsort1(list, off, s, comp)
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}
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s = d - c
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if s > 1 {
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qsort1(list, n-s, s, comp)
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}
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}
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func min(a int, b int) int {
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if a >= b {
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return b
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}
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return a
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}
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func max(a int, b int) int {
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if a < b {
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return b
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}
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return a
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}
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/**
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* Swaps x[a] with x[b].
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*/
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func swap(list []interface{}, a int, b int) {
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list[a], list[b] = list[b], list[a]
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}
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/**
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* Swaps x[a .. (a+n-1)] with x[b .. (b+n-1)].
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*/
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func vecswap(list []interface{}, a int, b int, n int) {
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for i := 0; i < n; i++ {
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swap(list, a, b)
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a++
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b++
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}
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}
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/**
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* Returns the index of the median of the three indexed integers.
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*/
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func med3(list []interface{}, a int, b int, c int, comp func(interface{}, interface{}) int) int {
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if comp(list[a], list[b]) < 0 {
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if comp(list[b], list[c]) < 0 {
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return b
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}
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if comp(list[a], list[c]) < 0 {
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return c
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}
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return a
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}
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if comp(list[b], list[c]) > 0 {
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return b
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}
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if comp(list[a], list[c]) > 0 {
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return c
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}
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return a
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}
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func rangeCopy(src []interface{}, low int, dest []interface{}, destLow int, length int) {
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for i := 0; i < length; i++ {
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dest[destLow+i] = src[low+i]
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}
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}
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/**
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* Src is the source array that starts at index 0
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* Dest is the (possibly larger) array destination with a possible offset
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* low is the index in dest to start sorting
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* high is the end index in dest to end sorting
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* off is the offset to generate corresponding low, high in src
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*/
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func mergeSort(src []interface{}, dest []interface{}, low int, high int, off int, comp func(interface{}, interface{}) int, depth int, maxDepth int, ch chan int) {
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defer func() {
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if ch != nil {
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ch <- 0
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}
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}()
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length := high - low
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// Insertion sort on smallest arrays
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if length < 7 {
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for i := low; i < high; i++ {
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for j := i; j > low && comp(dest[j-1], dest[j]) > 0; j-- {
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swap(dest, j, j-1)
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}
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}
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return
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}
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// Recursively sort halves of dest into src
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destLow := low
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destHigh := high
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low += off
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high += off
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/*
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* >>>：无符号右移运算符
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* expression1 >>> expresion2：expression1的各个位向右移expression2
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* 指定的位数。右移后左边空出的位数用0来填充。移出右边的位被丢弃。
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* 例如：-14>>>2； 结果为：1073741820
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*/
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mid := (low + high) >> 1
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if ch != nil {
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if depth < maxDepth {
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ch2 := make(chan int)
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go mergeSort(dest, src, low, mid, -off, comp, depth+1, maxDepth, ch2)
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go mergeSort(dest, src, mid, high, -off, comp, depth+1, maxDepth, ch2)
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waitCh(ch2, 2)
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} else {
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mergeSort(dest, src, low, mid, -off, comp, depth+1, maxDepth, nil)
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mergeSort(dest, src, mid, high, -off, comp, depth+1, maxDepth, nil)
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}
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} else {
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mergeSort(dest, src, low, mid, -off, comp, depth+1, maxDepth, ch)
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mergeSort(dest, src, mid, high, -off, comp, depth+1, maxDepth, ch)
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}
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// If list is already sorted, just copy from src to dest. This is an
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// optimization that results in faster sorts for nearly ordered lists.
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if comp(src[mid-1], src[mid]) <= 0 {
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rangeCopy(src, low, dest, destLow, length)
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return
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}
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// Merge sorted halves (now in src) into dest
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for i, p, q := destLow, low, mid; i < destHigh; i++ {
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if q >= high || p < mid && comp(src[p], src[q]) <= 0 {
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dest[i] = src[p]
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p++
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} else {
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dest[i] = src[q]
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q++
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}
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}
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}
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