159 lines
3.8 KiB
C
159 lines
3.8 KiB
C
#include <stdint.h>
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#include "parse.h"
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#include "printf.h"
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#include "cartesian.h"
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#include "array.h"
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struct position {
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char x;
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char y;
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};
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struct antenna {
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struct position position[8];
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char count;
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};
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#define FIRST_ANTENNA '0'
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#define LAST_ANTENNA 'z'
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#define ANTENNA_TYPES ((LAST_ANTENNA - FIRST_ANTENNA) + 1)
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void parse_antennas(const char * input, int length, struct antenna * antennas)
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{
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int x = 0;
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int y = 0;
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for (int i = 0; i < length; i++) {
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char c = input[i];
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if (c >= FIRST_ANTENNA && c <= LAST_ANTENNA) {
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struct antenna * ant = &antennas[c - FIRST_ANTENNA];
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ant->position[ant->count++] = (struct position){x, y};
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}
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if (c == '\n') {
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x = 0;
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y += 1;
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} else {
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x += 1;
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}
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}
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}
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struct position vector(struct position a, struct position b)
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{
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return (struct position){b.x - a.x, b.y - a.y};
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}
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void part1_antinodes(int width, int height,
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struct position p1, struct position p2,
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char * antinodes)
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{
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struct position slope = vector(p1, p2);
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struct position a[2] = {
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{
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p1.x - slope.x,
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p1.y - slope.y,
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},
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{
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p2.x + slope.x,
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p2.y + slope.y,
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}
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};
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for (int k = 0; k < 2; k++) {
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if (cartesian_inside(width, height, a[k].x, a[k].y)) {
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antinodes[a[k].y * width + a[k].x] = 1;
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}
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}
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}
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void interpolate_antinodes(int width,
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int height,
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struct position ant,
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struct position slope,
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char * antinodes)
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{
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int x = ant.x;
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int y = ant.y;
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while (true) {
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if (!cartesian_inside(width, height, x, y))
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break;
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antinodes[y * width + x] = 1;
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x -= slope.x;
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y -= slope.y;
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}
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}
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void part2_antinodes(int width, int height,
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struct position p1, struct position p2,
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char * antinodes)
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{
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struct position slope = vector(p1, p2);
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interpolate_antinodes(width, height, p1, (struct position){-slope.x, -slope.y}, antinodes);
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interpolate_antinodes(width, height, p2, (struct position){ slope.x, slope.y}, antinodes);
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}
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typedef void (* part_solver)(int width, int height,
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struct position p1, struct position p2,
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char * antinodes);
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void find_antinodes(int width, int height,
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const struct antenna * antennas,
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char * antinodes,
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part_solver func)
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{
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for (int t = FIRST_ANTENNA; t <= LAST_ANTENNA; t++) {
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const struct antenna * ant = &antennas[t - FIRST_ANTENNA];
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for (int i = 0; i < ant->count; i++) {
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for (int j = i + 1; j < ant->count; j++) {
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func(width, height,
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ant->position[i], ant->position[j],
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antinodes);
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}
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}
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}
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}
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int64_t _2024_day8_part1(const char * input, int length)
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{
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int stride = parse_stride(input, length);
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int height = parse_height(input, length);
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int width = stride - 1;
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struct antenna antennas[ANTENNA_TYPES];
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for (int i = 0; i < ANTENNA_TYPES; i++)
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antennas[i].count = 0;
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char antinodes[width * height];
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for (int i = 0; i < width * height; i++)
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antinodes[i] = 0;
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parse_antennas(input, length, antennas);
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find_antinodes(width, height, antennas, antinodes, part1_antinodes);
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return array_sum_char(antinodes, width * height);
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}
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int64_t _2024_day8_part2(const char * input, int length)
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{
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int stride = parse_stride(input, length);
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int height = parse_height(input, length);
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int width = stride - 1;
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struct antenna antennas[ANTENNA_TYPES];
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for (int i = 0; i < ANTENNA_TYPES; i++)
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antennas[i].count = 0;
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char antinodes[width * height];
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for (int i = 0; i < width * height; i++)
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antinodes[i] = 0;
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parse_antennas(input, length, antennas);
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find_antinodes(width, height, antennas, antinodes, part2_antinodes);
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return array_sum_char(antinodes, width * height);
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}
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