Initial commit with days 1, 2, and 3

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

.gitignore

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+
+# Created by https://www.toptal.com/developers/gitignore/api/python,vim
+# Edit at https://www.toptal.com/developers/gitignore?templates=python,vim
+
+### Python ###
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+#   For a library or package, you might want to ignore these files since the code is
+#   intended to run in multiple environments; otherwise, check them in:
+# .python-version
+
+# pipenv
+#   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
+#   However, in case of collaboration, if having platform-specific dependencies or dependencies
+#   having no cross-platform support, pipenv may install dependencies that don't work, or not
+#   install all needed dependencies.
+#Pipfile.lock
+
+# PEP 582; used by e.g. github.com/David-OConnor/pyflow
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/
+
+### Vim ###
+# Swap
+[._]*.s[a-v][a-z]
+!*.svg  # comment out if you don't need vector files
+[._]*.sw[a-p]
+[._]s[a-rt-v][a-z]
+[._]ss[a-gi-z]
+[._]sw[a-p]
+
+# Session
+Session.vim
+Sessionx.vim
+
+# Temporary
+.netrwhist
+*~
+# Auto-generated tag files
+tags
+# Persistent undo
+[._]*.un~
+
+# End of https://www.toptal.com/developers/gitignore/api/python,vim

README.md

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+# Advent of code 2021
+
+You should be able to run any of them by cd'ing into the directory and executing the script and
+passing the input file in through STDIN.
+
+Example:
+
+```
+cd day02
+./day02.py < input.txt
+```

day01/day01.py

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+#!/usr/bin/env python3
+import sys
+from typing import Sequence
+
+
+def part1(lines: Sequence[int]):
+    inc = 0
+    last = lines[0]
+    for line in lines[1:]:
+        if line > last:
+            inc += 1
+        last = line
+    print(f"{inc} increments")
+
+
+def part2(lines: Sequence[int]):
+    WINDOW_SIZE = 3
+    last = sum(lines[0:WINDOW_SIZE])
+    inc = 0
+    for i in range(1, len(lines) - WINDOW_SIZE + 1):
+        window = sum(lines[i:i+WINDOW_SIZE])
+        if window > last:
+            inc += 1
+        last = window
+    print(f"{inc} increments")
+
+
+lines = [int(line) for line in sys.stdin if line]
+print("Part 1")
+part1(lines)
+print("Part 2")
+part2(lines)

day02/day02.py

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+#!/usr/bin/env python3
+import sys
+from typing import Sequence, Tuple
+
+
+def part1(lines: Sequence[Tuple[str, int]]):
+    horz = 0
+    depth = 0
+    for direction, amount in lines:
+        if direction == "forward":
+            horz += amount
+        elif direction == "down":
+            depth += amount
+        elif direction == "up":
+            depth -= amount
+        else:
+            assert False, f"not sure how to handle {direction}"
+    print(f"horizontal position: {horz}")
+    print(f"depth: {depth}")
+    print(f"product: {depth * horz}")
+
+
+def part2(lines: Sequence[Tuple[str, int]]):
+    horz = 0
+    depth = 0
+    aim = 0
+    for direction, amount in lines:
+        if direction == "forward":
+            horz += amount
+            depth += aim * amount
+        elif direction == "down":
+            aim += amount
+        elif direction == "up":
+            aim -= amount
+        else:
+            assert False, f"not sure how to handle {direction}"
+    print(f"horizontal position: {horz}")
+    print(f"depth: {depth}")
+    print(f"product: {depth * horz}")
+
+
+lines = [(direction, int(amount)) for direction, amount in map(str.split, sys.stdin)]
+
+print("Part 1")
+part1(lines)
+print("Part 2")
+part2(lines)

day03/day03.py

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+#!/usr/bin/env python3
+import copy
+import sys
+from typing import Sequence
+
+
+def part1(lines: Sequence[int], bits=12):
+    gamma = 0
+    epsilon = 0
+    for bit in range(bits):
+        mask = 1 << (bits - bit - 1)
+        ones = 0
+        for line in lines:
+            if mask & line:
+                ones += 1
+        zeroes = len(lines) - ones
+        if ones > zeroes:
+            gamma |= mask
+        else:
+            epsilon |= mask
+    # Fun thing - epsilon rate is just the inversion of the gamma rate.
+    # However, python doesn't seem to support signed inversion so we just calculate it above. boo
+    print(f"gamma: {gamma} {bin(gamma)}")
+    print(f"epsilon: {epsilon} {bin(epsilon)}")
+    print(f"product: {gamma * epsilon}")
+
+
+def part2(lines: Sequence[int], bits=12):
+    oxygen = copy.deepcopy(lines)
+    carbon = copy.deepcopy(lines)
+    for bit in range(bits):
+        # Find the most common bit
+        if len(oxygen) > 1:
+            mask = 1 << (bits - bit - 1)
+            ones = 0
+            for line in oxygen:
+                if mask & line:
+                    ones += 1
+            zeroes = len(oxygen) - ones
+            if ones >= zeroes:
+                # Filter out oxygen numbers that don't have a 1 in this position
+                oxygen = [line for line in oxygen if line & mask]
+            else:
+                oxygen = [line for line in oxygen if not (line & mask)]
+
+        # Now do this on the carbon array
+        if len(carbon) > 1:
+            ones = 0
+            for line in carbon:
+                if mask & line:
+                    ones += 1
+            zeroes = len(carbon) - ones
+            if ones >= zeroes:
+                # Keep the *least* common
+                carbon = [line for line in carbon if not (line & mask)]
+            else:
+                carbon = [line for line in carbon if line & mask]
+    oxygen, = oxygen
+    carbon, = carbon
+    print(f"Oxygen: {oxygen}")
+    print(f"Carbon: {carbon}")
+    print(f"Product: {oxygen * carbon}")
+
+
+lines = [int(line, 2) for line in sys.stdin]
+
+print("Part 1")
+part1(lines)
+print("Part 2")
+part2(lines)