Greeting Lines

One greeting was a warm-up. Now do it for a whole list, and number the lines.

Go has no string concatenation operator you would want to use in a loop. The idiom is to build a slice of lines and then join them once, with strings.Join.

Task

Implement GreetAll(names []string) string in main.go. It returns one line per name, joined by "\n":

1. Hello, Ada!
2. Hello, Grace!
3. Hello, Alan!

The rules:

• Lines are numbered from 1, not from 0.
• An empty name is greeted as World, exactly like the last challenge: []string{"Ada", "", "Alan"} gives 2. Hello, World! in the middle.
• No names at all gives the empty string, "". A nil slice counts as no names.
• There is no trailing newline. Join puts the separator between elements, which is precisely what you want here.

Hints

• for i, name := range names gives you the index and the value at once. The line number is i + 1.

• fmt.Sprintf("%d. Hello, %s!", i+1, name) formats one line. %d is an integer, %s a string.

• Collect the lines in a []string and append to it, then strings.Join(lines, "\n").

• strings is not imported yet. Add it, and note that Go refuses to compile a file that imports a package it never uses:

  import (
  	"fmt"
  	"strings"
  )
  

• strings.Join of an empty slice is "", so the "no names" case needs no special handling.