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day 08

This commit is contained in:
Georgios Samaras 2024-12-08 11:37:39 +01:00
parent 545da2e0e6
commit 0f6f538786
3 changed files with 171 additions and 0 deletions
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50
day-08/input.txt Normal file
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................................y.................
............9.....Q................y..............
..................................................
..................................................
..........Q.......................x..N..1.........
.....9......6.e......................x.......j....
............e..x6Q9...............................
...........6..................................j...
...e....................................j.........
.............Q8.......................x..1........
.....w.......8...................y................
..n.......................y...................s...
.n................................................
.........n...............e........................
8..C..............r.....F......................j..
.......C......................................1..s
................n.u..................W...t........
......w..........r.........W..5J..................
.....p..............................J.............
.....T.................................d..........
......prw................uW.....Z.....t..6........
....p.r.....f............7........................
........C.f...q..................3.Y..............
.......w.f..........M.....C..5.......t............
....S..f.q.........................5..............
.............p......J........c................Z...
......................5...........................
....T...........u........D.....8........R.........
..0....T.............7M..........J....RZ..........
......t.Iu......................P.......W..Z......
...............D.......M.....i.......z..........s.
...........F..DM..q............R..................
........T....0............................c....s..
.E........0..............N........................
.......................................1........2X
..........Y....0.q....F..................X........
...............F.I..........................X.....
....U......z..............7i.........S..c.........
E.D..S...............................4.....2......
..S.........z..I......i.........m.............2...
.......E............I.....i..................R....
..................N...............................
....................................m.............
...Y...............P.............m...2............
................N...z................c............
.......................................4..........
........U.........P...............7..d..........4.
........................X....3....d...............
Y................P.U..........3...........d.......
...U..................................3...........

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#include "aoc.h"
#include <stdlib.h>
typedef struct {
i16 x, y;
u8 letter;
} Antenna;
static int
cmp_antennas(const void *a, const void *b) {
Antenna *aa = (Antenna *)a;
Antenna *bb = (Antenna *)b;
return aa->letter - bb->letter;
}
static i32
sum(const u8 *restrict values, isize len) {
i32 sum = 0;
for (isize i = 0; i < len; i++) {
sum += values[i];
}
return sum;
}
int main(int argc, char **argv) {
Arena *arena = make_arena(Megabytes(1));
str input = read_file(arena, argv[1]);
Grid grid = parse_grid(input, arena);
struct {
Antenna *data;
isize len, cap;
} antennas = {0};
for (isize y = 0; y < grid.height; y++) {
for (isize x = 0; x < grid.width; x++) {
u8 letter;
if ((letter = grid.grid[y * grid.width + x]) != '.') {
*push(&antennas, arena) = (Antenna){x, y, letter};
}
}
}
// sort/group antennas by frequency (i.e. letter)
qsort(antennas.data, antennas.len, sizeof(Antenna), cmp_antennas);
u8 *antinodes = ARENA_ALLOC_ARRAY(arena, u8, grid.width * grid.height);
isize group_start = 0;
for (isize i = 0; i < antennas.len; i++) {
if (antennas.data[i].letter != antennas.data[group_start].letter) {
group_start = i;
}
for (isize j = group_start; j < i; j++) {
ASSERT(antennas.data[i].letter == antennas.data[j].letter);
i32 dx = antennas.data[i].x - antennas.data[j].x;
i32 dy = antennas.data[i].y - antennas.data[j].y;
// first antinode
i32 antinode_x = antennas.data[i].x + dx;
i32 antinode_y = antennas.data[i].y + dy;
if (antinode_x >= 0 && antinode_y >= 0 && antinode_x < grid.width && antinode_y < grid.height) {
antinodes[antinode_y * grid.width + antinode_x] = 1;
}
// second antinode
antinode_x = antennas.data[j].x - dx;
antinode_y = antennas.data[j].y - dy;
if (antinode_x >= 0 && antinode_y >= 0 && antinode_x < grid.width && antinode_y < grid.height) {
antinodes[antinode_y * grid.width + antinode_x] = 1;
}
}
}
i32 part_1 = sum(antinodes, grid.width * grid.height);
printf("%d\n", part_1);
// Part 2
group_start = 0;
for (isize i = 0; i < antennas.len; i++) {
if (antennas.data[i].letter != antennas.data[group_start].letter) {
group_start = i;
}
for (isize j = group_start; j < i; j++) {
ASSERT(antennas.data[i].letter == antennas.data[j].letter);
i32 dx = antennas.data[i].x - antennas.data[j].x;
i32 dy = antennas.data[i].y - antennas.data[j].y;
i32 x = antennas.data[i].x;
i32 y = antennas.data[i].y;
while (x >= 0 && y >= 0 && x < grid.width && y < grid.height) {
antinodes[y * grid.width + x] = 1;
x += dx;
y += dy;
}
x = antennas.data[i].x;
y = antennas.data[i].y;
while (x >= 0 && y >= 0 && x < grid.width && y < grid.height) {
antinodes[y * grid.width + x] = 1;
x -= dx;
y -= dy;
}
}
}
i32 part_2 = sum(antinodes, grid.width * grid.height);
printf("%d\n", part_2);
}

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............
........0...
.....0......
.......0....
....0.......
......A.....
............
............
........A...
.........A..
............
............