Initial commit

2020/day12/day12.c

@@ -0,0 +1,119 @@
+#include <complex.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define PI
+
+struct instruction {
+  char action;
+  int value;
+};
+
+struct state {
+  double complex pos;
+  double complex dir;
+};
+
+void step1(struct state *st, struct instruction instr) {
+  switch (instr.action) {
+  case 'N': {
+    st->pos += instr.value * I;
+    break;
+  }
+  case 'S': {
+    st->pos -= instr.value * I;
+    break;
+  }
+  case 'E': {
+    st->pos += instr.value;
+    break;
+  }
+  case 'W': {
+    st->pos -= instr.value;
+    break;
+  }
+  case 'F': {
+    st->pos += instr.value * st->dir;
+    break;
+  }
+  case 'R': {
+    st->dir *= cexp(-instr.value * I * M_PI / 180);
+    break;
+  }
+  case 'L': {
+    st->dir *= cexp(instr.value * I * M_PI / 180);
+    break;
+  }
+  default:
+    printf("Invalid instruction %c %d\n", instr.action, instr.value);
+    break;
+  }
+}
+
+void step2(struct state *st, struct instruction instr) {
+  switch (instr.action) {
+  case 'N': {
+    st->dir += instr.value * I;
+    break;
+  }
+  case 'S': {
+    st->dir -= instr.value * I;
+    break;
+  }
+  case 'E': {
+    st->dir += instr.value;
+    break;
+  }
+  case 'W': {
+    st->dir -= instr.value;
+    break;
+  }
+  case 'F': {
+    st->pos += instr.value * st->dir;
+    break;
+  }
+  case 'R': {
+    st->dir *= cexp(-instr.value * I * M_PI / 180);
+    break;
+  }
+  case 'L': {
+    st->dir *= cexp(instr.value * I * M_PI / 180);
+    break;
+  }
+  default:
+    printf("Invalid instruction %c %d\n", instr.action, instr.value);
+    break;
+  }
+}
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    printf("Usage: %s <input file>\n", argv[0]);
+    return 0;
+  }
+
+  FILE *fp = fopen(argv[1], "r");
+  if (fp == NULL) {
+    printf("Could not open file %s\n", argv[1]);
+    return 1;
+  }
+
+  struct instruction in[1024];
+  int n = 0;
+  while (fscanf(fp, "%c%d\n", &in[n].action, &in[n].value) == 2) {
+    n++;
+  }
+  fclose(fp);
+
+  struct state st1 = {.pos = 0, .dir = 1};
+  struct state st2 = {.pos = 0, .dir = 10 + I};
+  for (int i = 0; i < n; ++i) {
+    step1(&st1, in[i]);
+    step2(&st2, in[i]);
+  }
+  printf("%d\n", (int)round(fabs(creal(st1.pos)) + fabs(cimag(st1.pos))));
+  printf("%d\n", (int)round(fabs(creal(st2.pos)) + fabs(cimag(st2.pos))));
+
+  return 0;
+}