Claw midpoint

c/2024/13/claw_contraption.c

@@ -0,0 +1,108 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include "../../lib/aoc.h"
+
+typedef struct Ratio {
+  long long num;
+  long long denom;
+} Ratio;
+
+typedef struct Line {
+  Ratio slope;
+  Ratio offset;
+} Line;
+
+Ratio ratio_subtract(Ratio r1, Ratio r2) {
+  Ratio r3;
+  r3.num= r1.num * r2.denom - r2.num * r1.denom;
+  r3.denom= r1.denom* r2.denom;
+  return r3;
+}
+
+Ratio ratio_divide(Ratio r1, Ratio r2) {
+  Ratio r3;
+  r3.num = r1.num * r2.denom;
+  r3.denom = r1.denom * r2.num;
+  return r3;
+}
+
+bool proper(Ratio r) {
+  return r.num % r.denom == 0;
+}
+
+Ratio intersect_x(Line l1, Line l2) {
+  Ratio left_side = ratio_subtract(l1.slope, l2.slope);
+  Ratio right_side = ratio_subtract(l2.offset, l1.offset);
+  Ratio divided = ratio_divide(right_side, left_side);
+  return divided;
+}
+
+int li_cost(int ax, int ay, int bx, int by, int px, int py) {
+  Line b_line;
+  b_line.slope.num = by;
+  b_line.slope.denom = bx;
+  b_line.offset.num = 0;
+  b_line.offset.denom = 1;
+
+  Line a_line;
+  a_line.slope.num = ay;
+  a_line.slope.denom = ax;
+  a_line.offset.num = -1 * ((px * ay) - (py * ax));
+  a_line.offset.denom = ax;
+  
+  Ratio r = intersect_x(b_line, a_line);
+
+  if (!proper(r)) {
+    printf("bzzt\n");
+    return 0;
+  }
+
+  long b_x_movement = (r.num / r.denom);
+  long b_cost = b_x_movement / bx;
+  long a_x_movement = px - b_x_movement;
+  long a_cost = a_x_movement / ax;
+  printf("%d\n", b_cost + a_cost);
+  return b_cost + a_cost;
+}
+
+int best_cost(int ax, int ay, int bx, int by, int px, int py) {
+  int best_cost_so_far = 0;
+  
+  for (int i = 0; i <= 100; i++) {
+    px -= ax;
+    py -= ay;
+    if (px % bx != 0 || py % by != 0) continue;
+    if (px / bx != py / by) continue;
+
+    int cost = (i + 1) * 3 + px / bx;
+    if (best_cost_so_far == 0 || best_cost_so_far > cost) best_cost_so_far = cost;
+  }
+
+  return best_cost_so_far;
+}
+
+int main() {
+  int ax, ay, bx, by, px, py;
+  char *line;
+
+  int cost = 0;
+  int cost_2 = 0;
+  while((line = aoc_read_line()) != NULL) {
+    sscanf(line, "Button A: X+%d, Y+%d", &ax, &ay);
+    sscanf(aoc_read_line(), "Button B: X+%d, Y+%d", &bx, &by);
+    sscanf(aoc_read_line(), "Prize: X=%d, Y=%d", &px, &py);
+    aoc_read_line();
+
+    cost += li_cost(ax, ay, bx, by, px, py);
+    cost_2 += li_cost(ax, ay, bx, by, px + 10000000000000, py + 10000000000000);
+  }
+
+  printf("Part 1: %d\n", cost);
+  printf("Part 2: %lld\n", cost_2);
+  
+  aoc_free();
+  return 0;
+}