The Go Programming Language Exercise 4.6.go

package main

import (
	"fmt"
	"unicode"
)

func removeDoubleSpaces(x []byte) []byte {
	var spaces int
	for i, v := range x {
		if unicode.IsSpace(rune(v)) {
			stop := i
			for _, vv := range x[i+1:] {
				if !unicode.IsSpace(rune(vv)) {
					break
				}
				stop++
			}
			spaces += len(x[i:stop])
			copy(x[i:], x[stop:])
		}
	}

	return x[:len(x)-spaces]
}

func main() {
	str := []byte("this is a  test  with  a few  double and triple   spaces   inserted throughout. and 4 spaces:    <- there")
	fmt.Printf("%s", removeDoubleSpaces(str))
}