95 lines
2.4 KiB
C
95 lines
2.4 KiB
C
#include "aoc.h"
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#include <limits.h>
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#include <ctype.h>
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typedef struct Vec2i {
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i64 x;
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i64 y;
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} Vec2i;
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static Vec2i
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parse_numbers(str line, Arena *arena) {
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bool x_set = false;
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Vec2i result = {0};
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for (isize i = 0; i < line.len; i++) {
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if (isdigit(line.data[i])) {
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isize end = i + 1;
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while (end < line.len && isdigit(line.data[end])) {
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end++;
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}
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str num_str = str_sub(line, i, end);
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if (!x_set) {
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result.x = (i32) parse_i64(num_str, *arena);
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x_set = true;
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}
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else {
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result.y = (i32) parse_i64(num_str, *arena);
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return result;
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}
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i = end;
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}
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}
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NOT_REACHABLE();
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}
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static bool
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solve(Vec2i a, Vec2i b, Vec2i p, Vec2i *solution) {
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i64 det = a.x * b.y - a.y * b.x;
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ASSERT(det != 0);
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i64 numerator_a = p.x * b.y - p.y * b.x;
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i64 numerator_b = p.y * a.x - p.x * a.y;
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bool solved = false;
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if ((numerator_a % det == 0) && (numerator_b % det == 0)) {
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i64 n_a = numerator_a / det;
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i64 n_b = numerator_b / det;
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if (n_a >= 0 && n_b >= 0) {
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solution->x = n_a;
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solution->y = n_b;
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solved = true;
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}
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}
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else {
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// no integer solution
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}
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return solved;
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}
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int main(int argc, char **argv) {
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Arena *arena = make_arena(Megabytes(1));
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str input = read_file(arena, argv[1]);
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str line;
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i64 part_1 = 0;
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i64 part_2 = 0;
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while (input.len > 0) {
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str a_line = str_next_token(&input, STR("\n"));
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str b_line = str_next_token(&input, STR("\n"));
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str prize_line = str_next_token(&input, STR("\n"));
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str empty_line = str_next_token(&input, STR("\n"));
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ASSERT(str_trim(empty_line).len == 0);
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Vec2i a = parse_numbers(a_line, arena);
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Vec2i b = parse_numbers(b_line, arena);
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Vec2i p = parse_numbers(prize_line, arena);
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Vec2i p_ = { p.x + 10000000000000ull, p.y + 10000000000000ull };
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#if 0
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printf("a: %ld %ld\n", a.x, a.y);
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printf("b: %ld %ld\n", b.x, b.y);
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printf("p: %ld %ld\n", p.x, p.y);
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printf("\n");
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#endif
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Vec2i n;
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if (solve(a, b, p, &n)) {
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part_1 += n.x * 3 + n.y;
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}
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if (solve(a, b, p_, &n)) {
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part_2 += n.x * 3 + n.y;
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}
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}
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printf("%ld\n", part_1);
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printf("%ld\n", part_2);
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}
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