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// Copyright (C) 2022-2023 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
// Package slices implements generic (type-parameterized) utilities
// for working with simple Go slices.
package slices
import (
"sort"
"golang.org/x/exp/constraints"
)
func Contains[T comparable](needle T, haystack []T) bool {
for _, straw := range haystack {
if needle == straw {
return true
}
}
return false
}
func RemoveAll[T comparable](haystack []T, needle T) []T {
for i, straw := range haystack {
if needle == straw {
return append(
haystack[:i],
RemoveAll(haystack[i+1:], needle)...)
}
}
return haystack
}
func RemoveAllFunc[T any](haystack []T, f func(T) bool) []T {
for i, straw := range haystack {
if f(straw) {
return append(
haystack[:i],
RemoveAllFunc(haystack[i+1:], f)...)
}
}
return haystack
}
func Reverse[T any](slice []T) {
for i := 0; i < len(slice)/2; i++ {
j := (len(slice) - 1) - i
slice[i], slice[j] = slice[j], slice[i]
}
}
func Max[T constraints.Ordered](a T, rest ...T) T {
ret := a
for _, b := range rest {
if b > a {
ret = b
}
}
return ret
}
func Min[T constraints.Ordered](a T, rest ...T) T {
ret := a
for _, b := range rest {
if b < a {
ret = b
}
}
return ret
}
func Sort[T constraints.Ordered](slice []T) {
sort.Slice(slice, func(i, j int) bool {
return slice[i] < slice[j]
})
}
// returns (a+b)/2, but avoids overflow
func avg(a, b int) int {
return int(uint(a+b) >> 1)
}
func min(a, b int) int {
if a < b {
return a
}
return b
}
func max(a, b int) int {
if a > b {
return a
}
return b
}
// Search searches the slice for a value for which `fn(slice[i]) = 0`.
//
// : + + + 0 0 0 - - -
// : ^ ^ ^
// : any of
//
// You can conceptualize `fn` as subtraction:
//
// func(straw T) int {
// return needle - straw
// }
func Search[T any](slice []T, fn func(T) int) (int, bool) {
beg, end := 0, len(slice)
for beg < end {
midpoint := avg(beg, end)
direction := fn(slice[midpoint])
switch {
case direction < 0:
end = midpoint
case direction > 0:
beg = midpoint + 1
case direction == 0:
return midpoint, true
}
}
return 0, false
}
// SearchLowest searches the slice for the left-most value for which
// `fn(slice[i]) = 0`.
//
// : + + + 0 0 0 - - -
// : ^
//
// You can conceptualize `fn` as subtraction:
//
// func(straw T) int {
// return needle - straw
// }
func SearchLowest[T any](slice []T, fn func(T) int) (int, bool) {
lastBad, firstGood, firstBad := -1, len(slice), len(slice)
for lastBad+1 < min(firstGood, firstBad) {
midpoint := avg(lastBad, min(firstGood, firstBad))
direction := fn(slice[midpoint])
switch {
case direction < 0:
firstBad = midpoint
case direction > 0:
lastBad = midpoint
default:
firstGood = midpoint
}
}
if firstGood == len(slice) {
return 0, false
}
return firstGood, true
}
// SearchHighest searches the slice for the right-most value for which
// `fn(slice[i]) = 0`.
//
// : + + + 0 0 0 - - -
// : ^
//
// You can conceptualize `fn` as subtraction:
//
// func(straw T) int {
// return needle - straw
// }
func SearchHighest[T any](slice []T, fn func(T) int) (int, bool) {
lastBad, lastGood, firstBad := -1, -1, len(slice)
for max(lastBad, lastGood)+1 < firstBad {
midpoint := avg(max(lastBad, lastGood), firstBad)
direction := fn(slice[midpoint])
switch {
case direction < 0:
firstBad = midpoint
case direction > 0:
lastBad = midpoint
default:
lastGood = midpoint
}
}
if lastGood < 0 {
return 0, false
}
return lastGood, true
}
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