This was a problem about checking for MD5 hashes beginning with a specified number of zeros. There is no trick, just iterate, compute, and check. Since I'm using python and this is a CPU bound problem, using concurrency would not speed up the solution at all. This is because the GIL lock prevents cpu-bound parallelism.
2015 Day 04 on AdventOfCode.com
Santa needs help mining some AdventCoins (very similar to bitcoins) to use as gifts for all the economically forward-thinking little girls and boys.
To do this, he needs to find MD5 hashes which, in hexadecimal, start with at least five zeroes. The input to the MD5 hash is some secret key (your puzzle input, given below) followed by a number in decimal. To mine AdventCoins, you must find Santa the lowest positive number (no leading zeroes: 1, 2, 3, ...) that produces such a hash.
For example:
- If your secret key is abcdef, the answer is 609043, because the MD5 hash of abcdef609043 starts with five zeroes (000001dbbfa...), and it is the lowest such number to do so.
- If your secret key is pqrstuv, the lowest number it combines with to make an MD5 hash starting with five zeroes is 1048970; that is, the MD5 hash of pqrstuv1048970 looks like 000006136ef....
Now find one that starts with six zeroes.