102 lines
2.6 KiB
C
102 lines
2.6 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdbool.h>
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#include "../../lib/aoc.h"
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typedef struct Ratio {
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long long num;
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long long denom;
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} Ratio;
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typedef struct Line {
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Ratio slope;
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Ratio offset;
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} Line;
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Ratio ratio_subtract(Ratio r1, Ratio r2) {
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Ratio r3;
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r3.num= r1.num * r2.denom - r2.num * r1.denom;
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r3.denom= r1.denom* r2.denom;
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return r3;
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}
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Ratio ratio_divide(Ratio r1, Ratio r2) {
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Ratio r3;
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r3.num = r1.num * r2.denom;
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r3.denom = r1.denom * r2.num;
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return r3;
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}
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bool proper(Ratio r) {
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return r.num % r.denom == 0;
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}
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Ratio intersect_x(Line l1, Line l2) {
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Ratio left_side = ratio_subtract(l1.slope, l2.slope);
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Ratio right_side = ratio_subtract(l2.offset, l1.offset);
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Ratio divided = ratio_divide(right_side, left_side);
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// printf("left: %lld/%lld, right: %lld/%lld, divided: %lld/%lld\n", left_side.num, left_side.denom, right_side.num, right_side.denom, divided.num, divided.denom);
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return divided;
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}
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long long li_cost(int ax, int ay, int bx, int by, long long px, long long py) {
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// printf("prize at %lld, %lld\n", px, py);
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Line b_line;
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b_line.slope.num = by;
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b_line.slope.denom = bx;
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b_line.offset.num = 0;
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b_line.offset.denom = 1;
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Line a_line;
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a_line.slope.num = ay;
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a_line.slope.denom = ax;
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a_line.offset.num = -1 * ((px * ay) - (py * ax));
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a_line.offset.denom = ax;
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Ratio r = intersect_x(b_line, a_line);
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if (!proper(r)) {
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// printf("bzzt\n");
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return 0;
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}
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long long b_x_movement = (r.num / r.denom);
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if (b_x_movement % bx != 0) return 0; // Fuuuuuuuuuuuuuuck this
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long long b_cost = b_x_movement / bx;
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long long a_x_movement = px - b_x_movement;
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if (a_x_movement % ax != 0) return 0; // Fuuuuuuuuuuuuuuck this
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long long a_cost = (a_x_movement / ax) * 3;
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// printf("b: %lld, a: %lld\n", b_x_movement, a_x_movement);
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// printf("b presses: %lld, a presses: %lld\n", b_x_movement / bx, a_x_movement / ax);
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if (b_x_movement < 0 || a_x_movement < 0) return 0;
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// printf("cost: %lld\n", b_cost + a_cost);
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return b_cost + a_cost;
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}
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int main() {
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int ax, ay, bx, by;
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int px, py;
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char *line;
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long long cost = 0;
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long long cost_2 = 0;
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while((line = aoc_read_line()) != NULL) {
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sscanf(line, "Button A: X+%d, Y+%d", &ax, &ay);
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sscanf(aoc_read_line(), "Button B: X+%d, Y+%d", &bx, &by);
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sscanf(aoc_read_line(), "Prize: X=%d, Y=%d", &px, &py);
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aoc_read_line();
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cost += li_cost(ax, ay, bx, by, px, py);
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cost_2 += li_cost(ax, ay, bx, by, px + 10000000000000, py + 10000000000000);
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// printf("\n");
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}
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printf("Part 1: %lld\n", cost);
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printf("Part 2: %lld\n", cost_2);
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aoc_free();
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return 0;
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}
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