99 lines
2.2 KiB
Go
99 lines
2.2 KiB
Go
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package fun
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import (
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"reflect"
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"sort"
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"github.com/BurntSushi/ty"
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)
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// QuickSort has a parametric type:
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//
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// func QuickSort(less func(x1 A, x2 A) bool, []A) []A
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//
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// QuickSort applies the "quicksort" algorithm to return a new sorted list
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// of `xs`, where `xs` is not modified.
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//
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// `less` should be a function that returns true if and only if `x1` is less
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// than `x2`.
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func QuickSort(less, xs interface{}) interface{} {
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chk := ty.Check(
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new(func(func(ty.A, ty.A) bool, []ty.A) []ty.A),
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less, xs)
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vless, vxs, tys := chk.Args[0], chk.Args[1], chk.Returns[0]
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var qsort func(left, right int)
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var partition func(left, right, pivot int) int
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xsind := Range(0, vxs.Len())
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qsort = func(left, right int) {
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if left >= right {
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return
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}
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pivot := (left + right) / 2
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pivot = partition(left, right, pivot)
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qsort(left, pivot-1)
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qsort(pivot+1, right)
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}
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partition = func(left, right, pivot int) int {
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vpivot := xsind[pivot]
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xsind[pivot], xsind[right] = xsind[right], xsind[pivot]
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ind := left
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for i := left; i < right; i++ {
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if call1(vless, vxs.Index(xsind[i]), vxs.Index(vpivot)).Bool() {
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xsind[i], xsind[ind] = xsind[ind], xsind[i]
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ind++
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}
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}
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xsind[ind], xsind[right] = xsind[right], xsind[ind]
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return ind
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}
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// Sort `xsind` in place.
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qsort(0, len(xsind)-1)
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vys := reflect.MakeSlice(tys, len(xsind), len(xsind))
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for i, xsIndex := range xsind {
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vys.Index(i).Set(vxs.Index(xsIndex))
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}
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return vys.Interface()
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}
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// Sort has a parametric type:
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//
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// func Sort(less func(x1 A, x2 A) bool, []A)
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//
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// Sort uses the standard library `sort` package to sort `xs` in place.
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//
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// `less` should be a function that returns true if and only if `x1` is less
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// than `x2`.
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func Sort(less, xs interface{}) {
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chk := ty.Check(
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new(func(func(ty.A, ty.A) bool, []ty.A)),
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less, xs)
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vless, vxs := chk.Args[0], chk.Args[1]
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sort.Sort(&sortable{vless, vxs, swapperOf(vxs.Type().Elem())})
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}
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type sortable struct {
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less reflect.Value
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xs reflect.Value
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swapper swapper
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}
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func (s *sortable) Less(i, j int) bool {
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ith, jth := s.xs.Index(i), s.xs.Index(j)
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return call1(s.less, ith, jth).Bool()
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}
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func (s *sortable) Swap(i, j int) {
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s.swapper.swap(s.xs.Index(i), s.xs.Index(j))
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}
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func (s *sortable) Len() int {
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return s.xs.Len()
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}
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