s/\t(?=\t)/\t0/g

Unfortunately, that regex doesn't work with other of the OPed example data strings that have leading and/or trailing tabs, e.g., "4\t4\t4\t\t\t4\t\t\t\t3\t" and "\t\t4\t4\t\t\t1\t\t\t\t". (It took me a while, but I finally figured out that all that whitespace was due to tab characters. I suspect that yueli711 changed the posted example data, too. Oh, well... :)