Things I learned during Advent of Code 2022

_aoc2022.md

Things I learned while doing Advent of Code 2022

• itertools.accumulate
• string.ascii_letters
• complex type
• max function
• locals
• Modular arithmetics
• Basic regex to find numbers
• SymPy library
• Working with set
• zip function
• Algorithms
  • BFS
  • DFS

accumulate.py

from itertools import accumulate

my_dir = ["/", "mydir/", "my_other_dir/", "test.txt"]

for n in accumulate(my_dir):
  print(n)
  
# /
# /mydir/
# /mydir/my_other_dir/
# /mydir/my_other_dir/test.txt

ascii.py

# Quick dict to find value of a letter
from string import ascii_letters

MAP_LETTER_PRIORITY = {}
for i, letter in enumerate(ascii_letters, start=1):
    MAP_LETTER_PRIORITY[letter] = i
# a -> 1
# b -> 2

bfs.py

# Calculate a BFS
def bfs(grid, start):
    queue = collections.deque([[start]])
    seen = set()
    while queue:
        path = queue.popleft()
        x, y = path[-1]
        if grid[y][x] == goal:
            return path
        for x2, y2 in ((x + 1, y), (x - 1, y), (x, y + 1), (x, y - 1)):
            if 0 <= x2 < width and 0 <= y2 < height and can_move(grid[y][x], grid[y2][x2]) and (x2, y2) not in seen:
                queue.append(path + [(x2, y2)])
                seen.add((x2, y2))

dfs.py

import functools

f = {}
f["AA"] = 1
f["BB"] = 2
f["CC"] = 7
g = {}
g["AA"] = ["BB", "CC"]
g["BB"] = ["AA", "CC"]
g["CC"] = ["BB", "AA"]


@functools.lru_cache(maxsize=None)
def maxflow(cur, opened, min_left):
    if min_left <= 0:
        return 0
    best = 0
    if cur not in opened:
        val = (min_left - 1) * f[cur]
        cur_opened = tuple(sorted(opened + (cur,)))
        for adj in g[cur]:
            if val != 0:
                best = max(best, val + maxflow(adj, cur_opened, min_left - 2))
            best = max(best, maxflow(adj, opened, min_left - 1))
    return best


result = maxflow("AA", (), 30)
print(result)

file.py

# To iterate on input file
# $ python a.py < input.txt

# If file is a one-line string
for c in input():
  print(c)
  
# If file is multilines
for line in open(0).read().splitlines():
  print(line)

groupby.py

message = "00011100"
result = ["".join(g) for k, g in groupby(c)]
print(result)

# ["000", "111", "00"]

imag.py

# Instead of
point = (5, 7)
x, y = point[0], point[1]

# Imaginary numbers
point = 5 + 7j
x, y = point.real, point.imag

locals.py

s = "root = 3 + 2"
exec(s)
print(locals()["root"])  # 5

max.py

a = 4
biggest = 0
# Instead of
if a > biggest:
  biggest = a
# Just do
biggest = max(biggest, a)

modular.py

# Modular arithmetics
# You can divide all numbers by their lcm (least common multiple) to keep numbers small
math.lcm(2, 5, 6)  # 30

neighbours.py

# Quickly check neighbours in grid

# Instead of
if x, y+1 == "X":
  win()
elif x+1, y == "X":
  win()
elif x, y-1 == "X":
  win()
elif x-1, y == "X":
  win()
  
# Just do
dirs = [(0, 1), (1, 0), (0, -1), (-1, 0)]
for dx, dy in dirs:
  new_x = x + dx
  new_y = y + dy
  if (new_x, new_y) == (5, 5):
    win()

regex.py

# Quickly find numbers in string
import re
result = [int(s) for s in re.findall(r"\b\d+\b", "dalue, 2 45")]
print(result)  # [2, 45]
result = list(map(int, re.findall(r"\d+", "dalue, truc2sd 45")))
print(result)  # [2, 45]

# Also catch negative numbers
result = list(map(int, re.findall(r"-?\d+", "dalue, truc2sd 45 -3")))
print(result)  # [2, 45, -3]

# Find 4-letters words
result = re.findall(r"[\w]{4}", "2 cats and 3 dogs")
print(result)  # ["cats", "dogs"]

set.py

# Overlap sets
a = set([1, 2, 3])
b = set([2, 3, 4])
print(a & b)  # {2, 3}
print(a | b)  # {1, 2, 3, 4}

sympy.py

from sympy.solvers import solve
from sympy import Symbol

x = Symbol("x")
print(solve("3*x - 3", x)[0])  # 1

tuple.py

# Easily add an element to a tuple
x = 1, 1, 1
x += (3,)
print(x)
# (1, 1, 1, 3)

zip.py

# Iterate two items at a time, sliding
a = [1, 2, 3, 4, 5, 6, 7, 8, 9]
for b, c in zip(a, a[1:]):
  print(b, c)
# 1, 2
# 2, 3
# ...

# In Python 3.10, you can even use itertools.pairwise
from itertools import pairwise
for b, c in pairwise(a):
  print(b, c)


for j, k, l in zip(*[a[i:] for i in range(3)]):
  print(j, k, l)

my_str = "abcdefghijklmnopqrstuvwxyz"
for x in range(4, len(my_str)):
    print(my_str[x - 4:x])
# abcd
# bcde
# ....