Day4 C

day4/c/day4.c

@@ -0,0 +1,88 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define LINE_MAX_LENGTH 256
+#define MAX_WINNING_NUMBERS 16
+#define MAX_SCRATCHED_NUMBERS 64
+#define MAX_FORESIGHT (MAX_WINNING_NUMBERS+1)
+#define NUM_0_CHARCODE 48
+#define NUM_9_CHARCODE NUM_0_CHARCODE + 9
+
+int read_numbers(char *p, char endchar, int dest[]) {
+    int count = 0;
+    while (*p != endchar && *(p+1) != endchar) {
+        // Advance till first digit
+        while (*p < NUM_0_CHARCODE || *p > NUM_9_CHARCODE) p++;
+        // Read number
+        sscanf(p, "%i", &dest[count]);
+        count++;
+        // Advance till endchar or separator
+        while (*p != ' ' && *p != endchar) p++;
+    }
+
+    return count;
+}
+
+int main() {
+    char *p, *buf, c;
+    int card_id;
+    int part1 = 0;
+
+    buf = (char *)malloc(LINE_MAX_LENGTH);
+    memset(buf, 0, LINE_MAX_LENGTH);
+    p = buf;
+
+    int winning_numbers[MAX_WINNING_NUMBERS], winning_numbers_num = 0;
+    int scratched_numbers[MAX_SCRATCHED_NUMBERS], scratched_numbers_num = 0;
+
+    int foresight[MAX_FORESIGHT], sum_scratchcards = 0;
+    memset(foresight, 0, MAX_FORESIGHT * sizeof(foresight[0]));
+
+    while ((c = getchar()) != EOF) {
+        *p++ = c;
+        if (c == '\n') {
+            p = buf;
+            sscanf(p, "Card %i", &card_id);
+
+            int num_cards = 1 + foresight[0];
+            sum_scratchcards += num_cards;
+
+            for (int i = 0; i < MAX_FORESIGHT-1; i++) {
+                foresight[i] = foresight[i+1];
+            }
+
+            // Advance till ':'
+            while (*p++ != ':');
+
+            winning_numbers_num = read_numbers(p, '|', winning_numbers);
+
+            while (*p++ != '|');
+
+            scratched_numbers_num = read_numbers(p, '\n', scratched_numbers);
+
+            int points = 0;
+            int scratchcards_won = 0;
+            for (int i = 0; i < scratched_numbers_num; i++) {
+                for (int j = 0; j < winning_numbers_num; j++) {
+                    if (scratched_numbers[i] == winning_numbers[j])  {
+                        points = points ? points * 2 : 1;
+                        scratchcards_won++;
+                    }
+                }
+            }
+
+            for (int i = 0; i < scratchcards_won; i++) {
+                foresight[i] += num_cards;
+            }
+            part1 += points;
+
+            memset(buf, 0, LINE_MAX_LENGTH);
+            p = buf;
+        }
+    }
+
+    free(buf);
+    printf("%i\n", part1);
+    printf("%i\n", sum_scratchcards);
+}