Day3

day3/c/day3.c

@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <regex.h>
+
+#define INPUT_MAX 1024*1024
+#define MAX_MATCHES 3
+
+int main() {
+    char *p, *buf, c;
+
+    buf = calloc(INPUT_MAX, sizeof(char));
+    p = buf;
+
+    regex_t regex, doit, dont;
+    regmatch_t matches[MAX_MATCHES];
+
+    regcomp(&regex, "mul\\(([0-9]{1,3}),([0-9]{1,3})\\)|do\\(\\)|don't\\(\\)", REG_EXTENDED);
+
+    while ((c = getchar()) != EOF) {
+        *p++ = c;
+    }
+
+    int sum = 0, sum2 = 0;
+    int enabled = 1;
+    p = buf;
+    for (;;) {
+        if(regexec(&regex, p, MAX_MATCHES, matches, 0)) {
+            break;
+        }
+
+        // mul matched
+        if (matches[1].rm_so != -1) {
+            // There will be 3 matches: 1 for the whole regex and 2 for the capture groups
+            int a, b;
+            sscanf(p + matches[1].rm_so, "%i", &a);
+            sscanf(p + matches[2].rm_so, "%i", &b);
+
+            sum += a * b;
+            if (enabled) {
+                sum2 += a * b;
+            }
+        } else {
+            if (*(p + matches[0].rm_so + 2) == 'n') {
+                enabled = 0;
+            } else {
+                enabled = 1;
+            }
+        }
+
+        p += matches[0].rm_eo;
+    }
+
+    regfree(&regex);
+    free(buf);
+
+    printf("%i\n", sum);
+    printf("%i\n", sum2);
+}