Advent of Code 2021

A simple repository for my solutions to the Advent of Code projects. These will be attempted in python, but I may branch out to other programming languages later to work on those skills.

Advent of Code: Day 1 - Sonar Sweeper

You are tasked with finding the keys to Santa's sleigh that were dropped in the ocean. You are on an elf-made submarine and are tasked with determining if every sweep on the sonar has either increased or decreased in depth since the last sweep.

From: Day 1

My Solution:

Open the input file and slurp it into memory.

with open('depth.txt') as infile:
    stuff = infile.read()

Split the list into individual values and take off annoying trailing character.

lis = stuff.split("\n")
depth = lis[:-1]

Convert list of strings to integers.

for i in range(len(depth)):
    depth[i] = int(depth[i])

Compare each entry pairwise to determine how often the depth increases.

count = 0
prev = depth[0]
for num in depth:
    if num > prev:
        count += 1
    prev = num
print(count)

Compare sets of three pairwise to determine how often the depth of sets of three increase.

count = 0
i = 0
prev = sum(depth[i:i+3])
while i < len(depth)-2:
    val = sum(depth[i:i+3])
    if val > prev:
        count +=1
    prev = val
    i += 1
print(count)

Advent of Code: Day 2 - Learning to Pilot a Submarine

Now that you understand how the sonar sweeper works, you must figure out how to pilot the submarine to avoid any untimely "meetings" with your surroundings. The three commands the submarine takes are up X, down X, and forward X, where "X" is a unit of measurement. In order to pilot the craft effectively, you must determine your final horizontal position and depth from a series of given commands.

From Day 2

My Solution:

Read in the input and separate each line

with open('inp.txt') as infile:
    lines = infile.read()

directions = lines.split("\n")
direcs = directions[:-1]

Make each line a new list of key, value pairs

new_list = []
horiz = 0
depth = 0
aim = 0
for line in direcs:
    new_list = line.split()

Given a key value pair, increase or decrease horiz, depth, and aim accordingly

    if new_list[0] == "forward":
        horiz += int(new_list[1])
        depth += int(new_list[1])*aim
    elif new_list[0] == "up":
        aim -= int(new_list[1])
    elif new_list[0] == "down":
        aim += int(new_list[1])
print(horiz*depth)

Advent of Code: Day 3 - Binary Diagnostic

The submarine started Ms. Behavin' so you decide to collect a diagnostic report. In order to do so you must sift through a boatload, or in your case a submarine-load, of binary data to determine the power consumption and life support rating.

From Day 3

My Solution

Read in the data and separate into individual lines

with open('val.txt') as infile:

This is an example of list comprehension that says make a new list "[]" called lines that contains the output from the read lines "infile.readlines()" from the file that have been stripped of their new line characters "x.rstrip()."

    lines = [x.rstrip() for x in infile.readlines()]

Initialize a list of zeros that is equal to the length of one row

l = []

for i in range(len(lines[0])):
   l.append(0)

Count if the first element of each line is either "0" or "1" and increment the respective list

for line in lines:
    for i in range(len(line)):
        if line[i] == "1":
            l[i] += 1
        else:
            l[i] -= 1

Compare each element of the list to each other to determine if "0" or "1" is the most common and print it

g = []
e = []
for i in range(len(l)):
    if l[i] > 0:
        g.append(1)
        e.append(0)
    else:
        g.append(0)
        e.append(1)

Converts each element of the list into a string to use the join() function (only operates on strings) that joins them with no delimiter. This is then turned back into an integer in the int() wrapper(?). Finally, the "2" is the second argument that turns decimal into binary using int().

gamma = int(''.join([str(i) for i in g]),2)
epsilon = int(''.join([str(i) for i in e]),2)

print("The power consumption rating is:", gamma*epsilon)

Defining functions that will be used to grab the column of numbers from the list, the most and least common bit from said columns

def column(i, lines):
    return [line[i] for line in lines]

def most_common(col):
    mc = 0
    num = 0
    for bit in col:
        if bit == "1":
            num += 1
        else:
            num -= 1
        if num >= 0:
            mc = 1
        else:
            mc = 0
    return mc

def least_common(col):
    lc = 0
    num = 0
    for bit in col:
        if bit == "1":
            num += 1
        else:
            num -= 1
    if num >= 0:
        lc = 0
    else:
        lc = 1
    return lc

Determines the most common bit from each column and trims the list to contain the element of the list with the most common bits

o2 = lines
for i in range(len(o2[0])):
    col = column(i, o2)
    b = most_common(col)
    o2 = [row for row in o2 if int(row[i]) == b]

Determines the least common bit from each column and trims the list to contain the element of the list with the least common bits. There is an additional "if" statement to overcome the problem that the last bit of the last element of the list is always the most common and would be deleted leaving an empty list

co2 = lines
for i in range(len(co2[0])):
    if len(co2) < 2:
        break
    col = column(i, co2)
    b = least_common(col)
    co2 = [row for row in co2 if int(row[i]) == b]


o2 = int(''.join([str(i) for i in o2]),2)
co2 = int(''.join([str(i) for i in co2]),2)

print("The life support rating is: ", o2*co2)