Solution to problem 13 in Python

src/Year_2021/P13.py

@@ -0,0 +1,184 @@
+# --- Day 13: Transparent Origami ---
+
+# You reach another volcanically active part of the cave. It would be nice if
+# you could do some kind of thermal imaging so you could tell ahead of time
+# which caves are too hot to safely enter.
+
+# Fortunately, the submarine seems to be equipped with a thermal camera! When
+# you activate it, you are greeted with:
+
+# Congratulations on your purchase! To activate this infrared thermal imaging
+# camera system, please enter the code found on page 1 of the manual.
+
+# Apparently, the Elves have never used this feature. To your surprise, you
+# manage to find the manual; as you go to open it, page 1 falls out. It's a
+# large sheet of transparent paper! The transparent paper is marked with random
+# dots and includes instructions on how to fold it up (your puzzle input).
+# For example:
+
+# 6,10
+# 0,14
+# 9,10
+# 0,3
+# 10,4
+# 4,11
+# 6,0
+# 6,12
+# 4,1
+# 0,13
+# 10,12
+# 3,4
+# 3,0
+# 8,4
+# 1,10
+# 2,14
+# 8,10
+# 9,0
+
+# fold along y=7
+# fold along x=5
+
+# The first section is a list of dots on the transparent paper. 0,0 represents
+# the top-left coordinate. The first value, x, increases to the right. The
+# second value, y, increases downward. So, the coordinate 3,0 is to the right
+# of 0,0, and the coordinate 0,7 is below 0,0. The coordinates in this example
+# form the following pattern, where # is a dot on the paper and . is an empty,
+# unmarked position:
+
+# ...#..#..#.
+# ....#......
+# ...........
+# #..........
+# ...#....#.#
+# ...........
+# ...........
+# ...........
+# ...........
+# ...........
+# .#....#.##.
+# ....#......
+# ......#...#
+# #..........
+# #.#........
+
+# Then, there is a list of fold instructions. Each instruction indicates a line
+# on the transparent paper and wants you to fold the paper up (for horizontal
+# y=... lines) or left (for vertical x=... lines). In this example, the first
+# fold instruction is fold along y=7, which designates the line formed by all
+# of the positions where y is 7 (marked here with -):
+
+# ...#..#..#.
+# ....#......
+# ...........
+# #..........
+# ...#....#.#
+# ...........
+# ...........
+# -----------
+# ...........
+# ...........
+# .#....#.##.
+# ....#......
+# ......#...#
+# #..........
+# #.#........
+
+# Because this is a horizontal line, fold the bottom half up. Some of the dots
+# might end up overlapping after the fold is complete, but dots will never
+# appear exactly on a fold line. The result of doing this fold looks like this:
+
+# #.##..#..#.
+# #...#......
+# ......#...#
+# #...#......
+# .#.#..#.###
+# ...........
+# ...........
+
+# Now, only 17 dots are visible.
+
+# Notice, for example, the two dots in the bottom left corner before the
+# transparent paper is folded; after the fold is complete, those dots appear in
+# the top left corner (at 0,0 and 0,1). Because the paper is transparent, the
+# dot just below them in the result (at 0,3) remains visible, as it can be seen
+# through the transparent paper.
+
+# Also notice that some dots can end up overlapping; in this case, the dots
+# merge together and become a single dot.
+
+# The second fold instruction is fold along x=5, which indicates this line:
+
+# #.##.|#..#.
+# #...#|.....
+# .....|#...#
+# #...#|.....
+# .#.#.|#.###
+# .....|.....
+# .....|.....
+
+# Because this is a vertical line, fold left:
+
+# #####
+# #...#
+# #...#
+# #...#
+# #####
+# .....
+# .....
+
+# The instructions made a square!
+
+# The transparent paper is pretty big, so for now, focus on just completing the
+# first fold. After the first fold in the example above, 17 dots are visible -
+# dots that end up overlapping after the fold is completed count as a single
+# dot.
+
+# How many dots are visible after completing just the first fold instruction on
+# your transparent paper?
+
+from copy import copy
+
+with open("files/P13.txt", "r") as f:
+    dots, folds = [line for line in f.read().strip().split("\n\n")]
+
+_dots = {tuple(map(int, row.split(","))) for row in dots.split("\n")}
+_folds = [(s[11] == "y", int(s[13:])) for s in folds.split("\n")]
+
+
+def fold(dim, value, dots):
+    folded = {dot for dot in dots if dot[dim] < value}
+    for x, y in dots - folded:
+        folded.add((x, 2 * value - y) if dim else (2 * value - x, y))
+    return folded
+
+
+def part_1():
+    ans = len(fold(*_folds[0], _dots))
+    print(f"There are {ans} dots visible after 1 fold")
+
+
+# --- Part Two ---
+
+# Finish folding the transparent paper according to the instructions. The
+# manual says the code is always eight capital letters.
+
+# What code do you use to activate the infrared thermal imaging camera system?
+
+
+def part_2():
+    dots = copy(_dots)
+    for dim, value in _folds:
+        dots = fold(dim, value, dots)
+
+    maxX, maxY = map(max, zip(*dots))
+
+    print("The code is: \n")
+    for y in range(maxY + 1):
+        for x in range(maxX + 1):
+            print("X" if (x, y) in dots else " ", end="")
+        print()
+
+
+if __name__ == "__main__":
+    part_1()
+    part_2()