2018/day10.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <stdarg.h>
   6 #include <stdbool.h>
   7 #include <assert.h>
   8
   9 void debug(const char *fmt, ...) {
  10   va_list ap;
  11   if (getenv("DEBUG")) {
  12     va_start(ap, fmt);
  13     vfprintf(stderr, fmt, ap);
  14     va_end(ap);
  15   }
  16 }
  17
  18 #define LIMIT 300
  19
  20 static struct data {
  21   int x;
  22   int y;
  23   int vx;
  24   int vy;
  25 } list[LIMIT];
  26
  27 void display(int count, int y, int minx, int maxx) {
  28   int i, j;
  29   for (i = minx; i <= maxx; i++) {
  30     char c = '.';
  31     for (j = 0; j < count; j++)
  32       if (list[j].y == y && list[j].x == i)
  33         c = '#';
  34     putchar(c);
  35   }
  36   putchar('\n');
  37 }
  38
  39 int main(int argc, char **argv) {
  40   size_t len = 0, count = 0;
  41   char *line;
  42   int i;
  43   int minx, miny, maxx, maxy, gap;
  44   int iters = 0;
  45
  46   /* Part 1 - read in lines */
  47   if (argc > 1)
  48     if (!(stdin = freopen(argv[1], "r", stdin))) {
  49       perror("failure");
  50       exit(2);
  51     }
  52
  53   while (getline(&line, &len, stdin) >= 0) {
  54     if (sscanf(line, "position=<%d,%d> velocity=<%d,%d> ", &list[count].x,
  55                &list[count].y, &list[count].vx, &list[count].vy) != 4) {
  56       fprintf(stderr, "bad input\n");
  57       exit(1);
  58     }
  59     ++count;
  60   }
  61   printf("Read %zu lines\n", count);
  62
  63   /* Part 2 - minimize gap */
  64   minx = miny = 100000;
  65   maxx = maxy = -100000;
  66   gap = 200000;
  67   for (i = 0; i < count; i++) {
  68     if (list[i].y > maxy)
  69       maxy = list[i].y;
  70     if (list[i].y < miny)
  71       miny = list[i].y;
  72     if (list[i].x > maxx)
  73       maxx = list[i].x;
  74     if (list[i].x < minx)
  75       minx = list[i].x;
  76   }
  77   printf("Starting with gap %d, column %d\n", maxy - miny, minx);
  78   do {
  79     iters++;
  80     gap = maxy - miny;
  81     minx = miny = 100000;
  82     maxx = maxy = -100000;
  83     for (i = 0; i < count; i++) {
  84       list[i].x += list[i].vx;
  85       list[i].y += list[i].vy;
  86       if (list[i].y > maxy)
  87         maxy = list[i].y;
  88       if (list[i].y < miny)
  89         miny = list[i].y;
  90       if (list[i].x > maxx)
  91         maxx = list[i].x;
  92       if (list[i].x < minx)
  93         minx = list[i].x;
  94     }
  95   } while (maxy - miny < gap);
  96   printf("After %d iters, gap is %d, column %d\n", iters, gap, minx);
  97
  98   /* Part 3 - undo last iteration, and print array */
  99   for (i = 0; i < count; i++) {
 100     list[i].x -= list[i].vx;
 101     list[i].y -= list[i].vy;
 102   }
 103   for (i = miny - 2; i < maxy + 2; i++)
 104     display(count, i, minx - 3, maxx + 3);
 105   return 0;
 106 }