Untitled

package main

import (
	"fmt"
	"sync"
)

func main() {
	ch := make(chan int)
	evenCh := make(chan struct{})
	oddCh := make(chan struct{})
	var wg sync.WaitGroup

	wg.Add(2)

	go even(ch, evenCh, oddCh, &wg)
	go odd(ch, oddCh, evenCh, &wg)

	// Start the sequence with even
	go func() {
		evenCh <- struct{}{}
	}()

	// Collect output
	go func() {
		wg.Wait()
		close(ch)

	}()

	for v := range ch {
		fmt.Println(v)
	}
}

func even(ch chan int, myTurn chan struct{}, nextTurn chan struct{}, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 0; i <= 20; i += 2 {
		<-myTurn
		ch <- i
		if i < 20 { // Avoid sending again after the last value
			nextTurn <- struct{}{}
		}
	}
}

func odd(ch chan int, myTurn chan struct{}, nextTurn chan struct{}, wg *sync.WaitGroup) {
	defer wg.Done()
	for i := 1; i <= 19; i += 2 {
		<-myTurn
		ch <- i
		nextTurn <- struct{}{}
	}

}