advent2025

Advent of Code 2025 Solutions
git clone git://bsandro.tech/advent2025
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day04.c (1288B)

      1 #include <stdio.h>
      2 #include <string.h>
      3 #include "cputime.h"
      4 
      5 // +1 on all sides
      6 #define W 141
      7 #define H 141
      8 
      9 #define LEN(x) (sizeof((x))/sizeof(*(x)))
     10 
     11 typedef char Map[H][W];
     12 typedef struct {
     13     int x, y;
     14 } Point;
     15 
     16 int count_adj(Map map, int x, int y) {
     17     int cnt = 0;
     18     Point points[] = {
     19         {x-1,y+1}, {x,y+1}, {x+1,y+1},
     20         {x-1,y  },          {x+1,y  },
     21         {x-1,y-1}, {x,y-1}, {x+1,y-1}
     22     };
     23     for (size_t p=0;p<LEN(points);++p) {
     24         if (map[points[p].y][points[p].x]=='@') cnt++;
     25     }
     26     return cnt;
     27 }
     28 
     29 int clean(Map map) {
     30     Map map1;
     31     memcpy(map1, map, sizeof(Map));
     32     int rem = 0;
     33     for (int y=1;y<H-1;++y) {
     34         for (int x=1;x<W-1;++x) {
     35             if (map1[y][x]=='@'&&count_adj(map1, x, y)<4) {
     36                 map[y][x]='.';
     37                 rem++;
     38             }
     39         }
     40     }
     41 
     42     return rem;
     43 }
     44 
     45 int main(void) {
     46     Map map = {0};
     47     int x = 1;
     48     int y = 1;
     49     for (int c=getchar();c!=EOF;c=getchar()) {
     50         if (c!='\n') map[y][x++] = c;
     51         else {
     52             y++;
     53             x=1;
     54         }
     55     }
     56 
     57     int p1 = 0;
     58     int p2 = 0;
     59     while (1) {
     60         int rem = clean(map);
     61         p2 += rem;
     62         if (p1==0) p1 = rem;
     63         if (rem==0) break;
     64     }
     65     printf("p1: %d\np2: %d\n", p1, p2);
     66     return 0;
     67 }