2024 day 8

2024/input/8.txt

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+.....y..........................p................r
+........I.........................................
+......................4.s.........................
+..........4.......................................
+....y.............................................
+......................................p.........r.
+..........0..s......N..................1.....p....
+..y........4.......................p..............
+...............0..................................
+..............0....t....N....h....................
+.............N....................................
+......j...................s............H...l..O...
+..........q.................H................O....
+..f...e.qj.....y...0..............................
+...........t..........................k..Q..r.....
+.........6................Q..s...x......W.........
+....2..b...e....t..4.........c.....xW.j...........
+...e....................w................1.....O..
+..e..j..5...........................c.............
+.........B..2...............MK................H...
+...2......b...g..X...q..........h...............O.
+...q...2..........m....k...i...............QV.x...
+...................i.........W.k.............HQ...
+........b...X...............D..........c...N......
+................................l..........h.....I
+.m...........g......l.......c.............3......V
+....X.......m........g...V.K...7......F.d.........
+.........b.X...U..........................C.......
+.....................l..............o.1....C......
+............u.............K..............3...d....
+......................i.T....f................V...
+..............................1.k.................
+.B.....E......9..m....K..5.M......................
+...P...............M...95....o..i........I........
+...............................S......3......wI...
+.....EP...........9........5..T.R.................
+.P..........v..9......f.............R.Co..w3......
+..........h...SG..v.E...7..f.T....................
+..........6..........L.................Y.......d..
+..........B...............U........D..............
+....B................U.....8..M....n...J..........
+.........................L................Fw......
+....L6E.P.................7.UG....J.....Y.D.......
+........t........v...SJ........n..d...............
+......................8v.....uG...................
+..................L.....n.........................
+...............T..............n......D............
+..............o.........8................J.Y.R....
+..................S...............u....F.......R..
+........6..............u.....7.8..........Y..F....

2024/js/day8.js

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+import { asLines } from './util.js';
+
+const map = asLines('../input/8.txt').map(l => l.split(""));
+
+const antennaByFreq = {};
+map.forEach((r, y) => r.forEach((freq, x) => {
+  if (freq == '.') return;
+  if (!antennaByFreq[freq]) antennaByFreq[freq] = [];
+  antennaByFreq[freq].push([x, y]);
+}));
+
+const valid = ([x, y]) => x >= 0 && x < map[0].length && y >= 0 && y < map.length;
+
+const anti = ([x, y], [dx, dy], distanceLimit) => {
+  const anti = new Set();
+  for (const an = [x, y]; valid(an); an[0] += dx, an[1] += dy) {
+    if (distanceLimit && an[0] - dx != x && an[1] - dy != y) continue;
+    anti.add(JSON.stringify(an));
+  }
+  return anti;
+};
+
+const antinodes = (distanceLimit) => {
+  const antinodes = new Set();
+  Object.entries(antennaByFreq).forEach(([_, coords]) => {
+    for (let i = 0; i < coords.length; i++) {
+      for (let j = 0; j < coords.length; j++) {
+        if (i == j) continue;
+        const [x1, y1] = coords[i];
+        const [x2, y2] = coords[j];
+        const dx = x2 - x1;
+        const dy = y2 - y1;
+        anti([x1, y1], [-dx, -dy], distanceLimit).forEach(a => antinodes.add(a));
+        anti([x2, y2], [dx, dy], distanceLimit).forEach(a => antinodes.add(a));
+      }
+    }
+  });
+  return antinodes;
+}
+
+console.log(`day8a ${antinodes(true).size}`);
+console.log(`day8b ${antinodes(false).size}`);