shad-go/utf8/reverse/reverse.go

//go:build !solution

package reverse

import (
	"strings"
	"unicode/utf8"
)

// inplace []rune reverse with 2 allocations
// first for runes slice and second for output
// func Reverse(input string) string {
// 	runes := []rune(input)
// 	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
// 		runes[i], runes[j] = runes[j], runes[i]
// 	}
// 	return string(runes)
// }

// string.Builder and utf8 decoding magic = 1 allocation
// overall more iterations but each one is faster,
// so its as fast as the inplace []rune reverse
func Reverse(input string) string {
	output := strings.Builder{}
	output.Grow(len(input))
	end := len(input)
	for end > 0 {
		r, n := utf8.DecodeLastRuneInString(input[:end])
		end -= n
		output.WriteRune(r)
	}
	return output.String()
}