advent2025

commit b882276f2387d250e46e6d88919c513aaf3bcbf3
parent 82d22cf2f4e37acc077b8a2f630e68c7a4f72933
Author: bsandro <email@bsandro.tech>
Date:   Thu,  4 Dec 2025 08:41:37 +0200

day04

Diffstat:
A
day04.c
 | 
68
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 68 insertions(+), 0 deletions(-)
diff --git a/day04.c b/day04.c
@@ -0,0 +1,68 @@
+#include <stdio.h>
+#include "cputime.h"
+
+// +1 on all sides
+#define W 141
+#define H 141
+
+#define LEN(x) (sizeof((x))/sizeof(*(x)))
+
+typedef char Map[H][W];
+typedef struct {
+    int x, y;
+} Point;
+
+int count_adj(Map map, int x, int y) {
+    int cnt = 0;
+    Point points[] = {
+        {x-1,y+1}, {x,y+1}, {x+1,y+1},
+        {x-1,y  },          {x+1,y  },
+        {x-1,y-1}, {x,y-1}, {x+1,y-1}
+    };
+    for (size_t p=0;p<LEN(points);++p) {
+        if (map[points[p].y][points[p].x]=='@') cnt++;
+    }
+    return cnt;
+}
+
+int clean(Map map) {
+    int rem = 0;
+    for (int y=1;y<H-1;++y) {
+        for (int x=1;x<W-1;++x) {
+            if (map[y][x]=='@'&&count_adj(map, x, y)<4) {
+                map[y][x]='.';
+                rem++;
+            }
+        }
+    }
+
+    return rem;
+}
+
+int main(void) {
+    Map map = {0};
+    int x = 1;
+    int y = 1;
+    for (int c=getchar();c!=EOF;c=getchar()) {
+        if (c!='\n') map[y][x++] = c;
+        else {
+            y++;
+            x=1;
+        }
+    }
+
+    int p1 = 0;
+    for (int y=1;y<H-1;++y) {
+        for (int x=1;x<W-1;++x) {
+            if (map[y][x]=='@'&&count_adj(map, x, y)<4) p1++;
+        }
+    }
+    int p2 = 0;
+    while (1) {
+        int rem = clean(map);
+        p2 += rem;
+        if (rem==0) break;
+    }
+    printf("p1: %d\np2: %d\n", p1, p2);
+    return 0;
+}