Separate two numbers

I would like to separate number by space so that

121231212
222111212

would be

1 2 1 2 3 1 2 1 2
2 2 2 1 1 1 2 1 2

Thanks!

echo '12345' | sed 's/./ & /g'

quick and dirty...

echo 121231212 | sed -e 's/\(.\)/\1 /g'

This will put a space after your last number however.