Program runs out of memory using GHC 7.6.3

[David Spies]

I have a program I submitted for a Kattis problem:
https://open.kattis.com/problems/digicomp2
But I got memory limit exceeded.  I downloaded the test data and ran the
program on my own computer without problems.  Eventually I found out that
when compiling with GHC 7.6.3 (the version Kattis uses) rather than 7.8.3,
this program runs out of memory.
Can someone explain why it only works on the later compiler?  Is there a
workaround so that I can submit to Kattis?

Thanks,
David
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