This is inspired by one of Downgoat's questions in Sandbox, where I suggested that he include April 31 as Pi day for people who use day/month format, only for him to inform me that there is no April 31!
Given a date string in month/day format that might be invalid, output the correct date using rollover. (First rollover the month, then rollover the day).
"15/43" - This reads as the 43rd day of the 15th month. First, we roll over the month to the next year, so we end up with 3 (March). Now, since March only has 31 days, we rollover the extra days to April, so we output the actual date as "4/12" (April 12th).
"3/16" - This is a valid date (March 16th). Return it as is.
"12/64" - Ah, so many fond memories from December 64th... December has 31 days, January has 31 days, so what I really mean is "2/2" (February 2nd).
"19/99" - First, the 19 becomes a 7 (July). July has 31 days, August has 31 days, September has 30 days, so the output is "10/7" (October 7th).
"1/99999" - A year has 365 days. 99999 (mod 365) = 354. The 354 day of the year is "12/20".
"9999999/10" - Apparently, 9999999 (mod 12) = 3, so this is "3/10" (March 10th).
Input month is an integer > 0. Input day is an integer > 0. Year never needs to be specified, as such there are no leap years to deal with.
As I think it would overly simplify the challenge, calendar functions, such as those in the Java Calendar class, are banned. Date parsing/formatting functions are still allowed though.