3 files changed, 102 insertions, 0 deletions
diff --git a/04/Makefile b/04/Makefile
new file mode 100644
index 0000000..a8f700f
--- /dev/null
+++ b/04/Makefile
@@ -0,0 +1,13 @@
+all: part1 part2
+
+part1: part1.c
+	gcc -g part1.c -o part1 -lalgds
+
+part2: part2.c
+	gcc -g part2.c -o part2 -lalgds
+
+1: part1
+	cat input | ./part1
+
+2: part2
+	cat input | ./part2
+\ No newline at end of file
diff --git a/04/part1.c b/04/part1.c
new file mode 100644
index 0000000..0603946
--- /dev/null
+++ b/04/part1.c
@@ -0,0 +1,89 @@
+#include <algds/str.h>
+#include <algds/vec.h>
+
+StringVector readmap() {
+    StringVector map;
+    StringVector_init(&map);
+    while (1) {
+        char *l = fgetline(stdin);
+        if (!l) {
+            return map;
+        }
+        char *nl = str_strip(l);
+        free(l);
+        l = nl;
+        if (strlen(l) == 0) {
+            return map;
+        }
+        StringVector_push_back(&map, l);
+    }
+    return map;
+}
+
+char map_read(StringVector *map, int x, int y) {
+    int height = StringVector_len(map);
+    if (height == 0) {
+        return '\0';
+    }
+    int width = strlen(*StringVector_ref(map, 0));
+    if (x >= width || x < 0) {
+        return '\0';
+    }
+    if (y >= height || y < 0) {
+        return '\0';
+    }
+    return (*StringVector_ref(map, y))[x];
+}
+
+
+bool is_paper(StringVector *map, int x, int y) {
+    return map_read(map, x, y) == '@';
+}
+
+int count_adjacent(StringVector *map, int x, int y) {
+    int count = 0;
+    if (is_paper(map, x - 1, y - 1)) {
+        count++;
+    }
+    if (is_paper(map, x - 1, y)) {
+        count++;
+    }
+    if (is_paper(map, x, y - 1)) {
+        count++;
+    }
+    if (is_paper(map, x + 1, y + 1)) {
+        count++;
+    }
+    if (is_paper(map, x + 1, y)) {
+        count++;
+    }
+    if (is_paper(map, x, y + 1)) {
+        count++;
+    }
+    if (is_paper(map, x + 1, y - 1)) {
+        count++;
+    }
+    if (is_paper(map, x - 1, y + 1)) {
+        count++;
+    }
+    return count;
+}
+
+int main() {
+    StringVector map = readmap();
+    int height = StringVector_len(&map);
+    int width = strlen(*StringVector_ref(&map, 0));
+    int res = 0;
+    for (int x = 0; x < width; x++) {
+        for (int y = 0; y < height; y++) {
+            if (map_read(&map, x, y) != '@') {
+                continue;
+            }
+            if (count_adjacent(&map, x, y) < 4) {
+                res++;
+            }
+        }
+    }
+    printf("%d\n", res);
+    return 0;
+}
+\ No newline at end of file
diff --git a/04/part2.c b/04/part2.c
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/04/part2.c