1 2 3 4 5
n = ["998700", "1001900", "009987", "0010019"] puts n.map { |i| i =~ /^0*([0-9]+?)0*$/ "00" + $1 + "0" * [0, 6 - $1.length].max }
1 2 3 4
00998700 00100190 00998700 00100190