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aoc_2024_8_1.c - aoc - Advent of Code challenges
	aoc Advent of Code challenges
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aoc_2024_8_1.c (2468B)
      1 #include <stdlib.h>
      2 #include <stdbool.h>
      3 #include <string.h>
      4 #include <assert.h>
      5 
      6 #define ANTENNA_SIZE 500
      7 #define ANTINODE_SIZE 500
      8 
      9 typedef struct {
     10   int y;
     11   int x;
     12 } pos_t;
     13 
     14 typedef struct {
     15   char id;
     16   pos_t pos;
     17 } antenna_t;
     18 
     19 long perform(char *data) {
     20   size_t len = strlen(data);
     21   size_t rows = 0;
     22   size_t cols = 0;
     23   size_t antennas_len = 0;
     24   antenna_t antennas[ANTENNA_SIZE];
     25   for (size_t i = 0; i < len; i++) {
     26     if (data[i] == '\n') {
     27       if (rows == 0) {
     28         cols = i;
     29       }
     30       rows++;
     31     }
     32   }
     33   for (size_t i = 0; i < len; i++) {
     34     char c = data[i];
     35     if (c != '\n' && c != '.') {
     36       int y = i / (cols + 1);
     37       int x = i % (cols + 1);
     38       assert(antennas_len < ANTENNA_SIZE);
     39       antennas[antennas_len] = (antenna_t) {
     40         .id = c,
     41         .pos = { y, x },
     42       };
     43       antennas_len++;
     44     }
     45   }
     46   size_t antinodes_len = 0;
     47   pos_t antinodes[ANTINODE_SIZE];
     48   for (size_t i = 0; i < antennas_len; i++) {
     49     for (size_t j = i + 1; j < antennas_len; j++) {
     50       antenna_t a = antennas[i];
     51       antenna_t b = antennas[j];
     52       if (a.id == b.id) {
     53         pos_t delta = {
     54           abs(a.pos.y - b.pos.y),
     55           abs(a.pos.x - b.pos.x),
     56         };
     57         pos_t node_a;
     58         pos_t node_b;
     59         if (a.pos.y > b.pos.y) {
     60           node_a.y = a.pos.y + delta.y;
     61           node_b.y = b.pos.y - delta.y;
     62         }
     63         else {
     64           node_a.y = a.pos.y - delta.y;
     65           node_b.y = b.pos.y + delta.y;
     66         }
     67         if (a.pos.x > b.pos.x) {
     68           node_a.x = a.pos.x + delta.x;
     69           node_b.x = b.pos.x - delta.x;
     70         }
     71         else {
     72           node_a.x = a.pos.x - delta.x;
     73           node_b.x = b.pos.x + delta.x;
     74         }
     75         assert(antinodes_len < ANTINODE_SIZE);
     76         antinodes[antinodes_len] = node_a;
     77         antinodes_len++;
     78         assert(antinodes_len < ANTINODE_SIZE);
     79         antinodes[antinodes_len] = node_b;
     80         antinodes_len++;
     81       }
     82     }
     83   }
     84   long count = 0;
     85   for (size_t i = 0; i < antinodes_len; i++) {
     86     pos_t antinode = antinodes[i];
     87     if (
     88       antinode.y < 0 || antinode.x < 0 ||
     89       antinode.y >= (int) rows || antinode.x >= (int) cols
     90     ) {
     91       continue;
     92     }
     93     bool is_unique = true;
     94     for (size_t j = i + 1; j < antinodes_len; j++) {
     95       if (antinode.y == antinodes[j].y && antinode.x == antinodes[j].x) {
     96         is_unique = false;
     97         break;
     98       }
     99     }
    100     if (is_unique) {
    101       count++;
    102     }
    103   }
    104   return count;
    105 }