Advent of Code 2015 Day 25

— Day 25: Let It Snow —

We need to fix Santa’s weather machine with some code generation.

Your puzzle input contains the message on the machine’s console. What code do you give the machine?

# actual requirement
_r = 3010
_c = 3019

# testing requirement
# _r = 301
# _c = 309

This seems like straight forward arithmetic, but I think I need to use triangular numbers to easily calculate where the 3010th row and 3019th column would be. It’s not just 3010 * 3019, but I’ll need to produce at least that many numbers.

Since the sequence is sequential, I can’t take any shortcuts to actually get to the number, so let’s just loop through and keep track of the position. Probably: no doubt there’s some kind of shortcut.

# first value, multiply by m, then divide by d
num = 20151125
m = 252533
d = 33554393
i = 0

pos = {'r': 1, 'c': 1}

while i < 10**8: 
    num = (num * m) % 33554393
    i += 1
    if pos['r'] == 1: 
        pos['r'] = pos['c'] + 1
        pos['c'] = 1
    else: 
        pos['r'] -= 1
        pos['c'] += 1
    
    # print(str(num) + ', ' + str(pos))
    # check for finish condition
    if pos['r'] == _r and pos['c'] == _c:
        break

print(str(num) + ', ' + str(pos))

# 8997277

8997277, {'r': 3010, 'c': 3019}

— Part Two —

Do all of the other days :)