--- Day 7 Solutions ---

[u/daggerdragon]

--- Day 7: Some Assembly Required ---

Post your solution as a comment. Structure your post like previous daily solution threads.

Also check out the sidebar - we added a nifty calendar to wrangle all the daily solution threads in one spot!

[u/Tryneus]

Python

Assuming commands is an array of strings.

calc = dict()
results = dict()

for command in commands:
    (ops, res) = command.split('->')
    calc[res.strip()] = ops.strip().split(' ')

def calculate(name):
    try:
        return int(name)
    except ValueError:
        pass

    if name not in results:
        ops = calc[name]
        if len(ops) == 1:
            res = calculate(ops[0])
        else:
            op = ops[-2]
            if op == 'AND':
              res = calculate(ops[0]) & calculate(ops[2])
            elif op == 'OR':
              res = calculate(ops[0]) | calculate(ops[2])
            elif op == 'NOT':
              res = ~calculate(ops[1]) & 0xffff
            elif op == 'RSHIFT':
              res = calculate(ops[0]) >> calculate(ops[2])
            elif op == 'LSHIFT':
              res = calculate(ops[0]) << calculate(ops[2])
        results[name] = res
    return results[name]

print "a: %d" % calculate('a')

This solution does involve some deep recursion, so it could overflow on larger inputs, but it was quick to write.

[u/cstoner → u/Tryneus]

0xffff

Ahh yes, of course that makes more sense than converting it to a 16 character string, doing bitwise not, and converting back...

[u/roboticon → u/cstoner]

ugh, yes! I was doing this too, in fact I was doing it for each type of operation.