9.md

Day 9

A quick one, I felt like I could have done it quicker if I wasn't on my laptop using a mouse without a mousepad.

	Part 1	Part 2	Total
Time	7:58	2:37	10:35

Part 1

This one is a kind of "just do it" type of problem. I'll explain anyway.

I first created a function to compute the difference between each step, then I created another function to keep doing that over and over until a list of all zeros is reached. Finally, I loop through these differences and solve for X where x - val_i = val_i+1, rearrange x = val_i + val_i+1. Then sum them up and there you have it!

from helpers.datagetter import aocd_data_in

din, aocd_submit = aocd_data_in(split=True, numbers=True)
ans = 0


def get_diff(l):
    o = []
    for i in range(len(l)-1):
        o.append(l[i+1] - l[i])
    return o


def get_diffs(l):
    o = [l]
    while any([x != 0 for x in l]):
        l = get_diff(l)
        o.append(l)
    return o


for line in din:
    diffs = get_diffs(line)
    diffs[-1].append(0)
    for i in range(len(diffs)-2, -1, -1):
        diffs[i].append(diffs[i+1][-1] + diffs[i][-1])
    ans += diffs[0][-1]

aocd_submit(ans)

Part 2

A very simple modification for Part 2, I was just having trouble rearranging val_i - x = val_i+1 at midnight. I was happy with the delta, but it could have been way better if I was thinking better! Just switch that and the values to be inserted at the beginning and that's all you need.

I could have just kept the appends the same and just changed which values I was referencing for the current "row" but the way it is currently done keeps it in proper order with the problem, so I'm fine with that.

from helpers.datagetter import aocd_data_in

din, aocd_submit = aocd_data_in(split=True, numbers=True)
ans = 0

def get_diff(l):
    o = []
    for i in range(len(l)-1):
        o.append(l[i+1] - l[i])
    return o


def get_diffs(l):
    o = [l]
    while any([x != 0 for x in l]):
        l = get_diff(l)
        o.append(l)
    return o


for line in din:
    diffs = get_diffs(line)
    diffs[-1].insert(0, 0)
    for i in range(len(diffs)-2, -1, -1):
        diffs[i].insert(0, diffs[i][0] - diffs[i+1][0])
    ans += diffs[0][0]

aocd_submit(ans)