From 8f0bc54b7c90c7cb495a93cb687ff57afddf4528 Mon Sep 17 00:00:00 2001
From: Sebastian Mark <smark@posteo.net>
Date: Sun, 8 Dec 2024 20:20:40 +0100
Subject: [PATCH] add 2024/day8

---
 2024/08/main.py | 94 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 2024/08/main.py

diff --git a/2024/08/main.py b/2024/08/main.py
new file mode 100644
index 0000000..0f23a1d
--- /dev/null
+++ b/2024/08/main.py
@@ -0,0 +1,94 @@
+#!/usr/bin/env python
+# -*- encoding: utf-8; py-indent-offset: 4 -*-
+
+# Author: Sebastian Mark
+# CC-BY-SA (https://creativecommons.org/licenses/by-sa/4.0/deed.de)
+
+# pylint: disable=missing-module-docstring,missing-function-docstring,consider-using-f-string
+
+import re
+
+
+def readinput():
+    with open("input", "r", encoding="utf-8") as file:
+        lines = [line.strip("\n") for line in file.readlines()]
+    return lines
+
+
+def get_antinodes_for_pair(city: list, pos: tuple, twin: tuple, part: int) -> set:
+    width = len(city[0])
+    height = len(city)
+
+    antinodes_for_pair = set()
+
+    # distance between pairs
+    dy = pos[0] - twin[0]
+    dx = pos[1] - twin[1]
+
+    # add antinode(s) above upper antenna
+    nxty = pos[0] + dy
+    nxtx = pos[1] + dx
+    while 0 <= nxty < height and 0 <= nxtx < width:
+        antinodes_for_pair.add((nxty, nxtx))
+        if part == 1:
+            break
+        nxty += dy
+        nxtx += dx
+
+    # add antinode(s) below lower antenna
+    nxty = twin[0] - dy
+    nxtx = twin[1] - dx
+    while 0 <= nxty < height and 0 <= nxtx < width:
+        antinodes_for_pair.add((nxty, nxtx))
+        if part == 1:
+            break
+        nxty -= dy
+        nxtx -= dx
+
+    return antinodes_for_pair
+
+
+def get_antinodes_for_freq(city: list, freq: str, pos: tuple, part: int) -> set:
+    starty = pos[0]
+    antinodes_for_freq = set()
+
+    # search downwards for twins
+    twins = []
+    if starty <= len(city):
+        for y in range(starty + 1, len(city)):
+            x = city[y].find(freq)
+            if x >= 0:
+                twins.append((y, x))
+
+    for twin in twins:
+        antinodes_for_freq |= get_antinodes_for_pair(city, pos, twin, part)
+
+    return antinodes_for_freq
+
+
+def get_antinodes(city: list, part: int) -> set:
+    antinodes = set()
+
+    # serch city for antennas
+    for y, street in enumerate(city):
+        antennas = re.finditer(r"([a-zA-Z0-9])", street)
+        for antenna in antennas:
+            freq = antenna.group()
+            pos = (y, antenna.start())
+            antinodes |= get_antinodes_for_freq(city, freq, pos, part)
+            if part == 2:
+                antinodes.add(pos)
+
+    return antinodes
+
+
+def main():
+    city = readinput()
+
+    for part in [1, 2]:
+        antinodes = get_antinodes(city, part)
+        print("Unique antinodes (part%d): %d" % (part, len(antinodes)))
+
+
+if __name__ == "__main__":
+    main()