Advent of Code 2022 Day 20

— Day 20: Grove Positioning System —

We’re going to the grove where the star fruit grows, but we need to figure out where that is.

Mix your encrypted file exactly once. What is the sum of the three numbers that form the grove coordinates?

with open('data-2022-20.txt', 'r') as f:
    inp = f.read().splitlines()

We need to keep track of the original order, and the list of numbers being mixed.

orig = [int(x) for x in inp]
mix = [int(x) for x in inp]

# print(mix)

for o in orig: 
    # find the current position of this one in mix
    old_pos = mix.index(o)
    # print(o, old_pos)
    # work out the new index
    new_pos = old_pos + o
    if new_pos > len(orig): 
        new_pos = new_pos - len(orig) + 1
    if new_pos == 0: 
        new_pos = len(orig)
    # move
    mix.insert(new_pos, mix.pop(old_pos))
    # print to check
    # print(mix)

Work out position 1000, 2000, 3000 after the value 0.

# answer counter
sums = 0

# location of zero
zz = mix.index(0)
# zz

# length of array for convenience
ll = len(mix)

# need each of these permissions
for ii in [1000, 2000, 3000]: 
    # don't need to loop, just find the position assuming we have looped around
    rr = ii % ll
    # can't be bigger than the array, take the length off
    # because we start from position 0
    rr += zz
    if rr > ll: 
        rr -= len(mix)
    # print and record
    # mix[rr]
    sums += mix[rr]

sums

# -9675 incorrect
# 3598 too low

-9675