How to make this fast and efficient is an interesting programming problem. There are 100 permutations of 2 digit numbers: perhaps one could pre-determine the i

How to make this fast and efficient is an interesting programming problem. There are 100 permutations of 2 digit numbers: perhaps one could pre-determine the index of the first N (1,000?) instances of each of these 100 numbers and scan starting at these locations before falling back on a substring search. Filter for valid dates. Take advantage of the fact that the end of the substring will most likely fall in the range 70-90. Etc...