Day9 C

day9/c/day9.c

@@ -0,0 +1,92 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define LINE_MAX_LENGTH 256
+#define MAX_VALUE_PER_HISTORY 64
+
+int extrapolate(int history[], int history_num);
+int extrapolate_backwards(int history[], int history_num);
+
+int main() {
+    char *p, *buf, c;
+
+    buf = (char *)malloc(LINE_MAX_LENGTH);
+    memset(buf, 0, LINE_MAX_LENGTH);
+    p = buf;
+
+    int part1 = 0, part2 = 0;
+
+    while ((c = getchar()) != EOF) {
+        *p++ = c;
+        if (c == '\n') {
+            int history[MAX_VALUE_PER_HISTORY], history_num = 0;
+            p = buf;
+
+            while (*p != '\0') {
+                sscanf(p, "%i", &history[history_num]);
+                history_num++;
+                while(*p != ' ' && *p != '\n') p++;
+                p++;
+            }
+
+            part1 += extrapolate(history, history_num);
+            part2 += extrapolate_backwards(history, history_num);
+
+            memset(buf, 0, LINE_MAX_LENGTH);
+            p = buf;
+        }
+    }
+
+    printf("%i\n", part1);
+    printf("%i\n", part2);
+    free(buf);
+}
+
+int extrapolate(int history[], int history_num) {
+    int zeros = 1;
+    for (int i = 0; i < history_num; i++) {
+        if (history[i] != 0) {
+            zeros = 0;
+            break;
+        }
+    }
+
+    if (zeros) {
+        return 0;
+    }
+
+    int *new_history = (int*)malloc((history_num - 1) * sizeof(int));
+
+    for (int i = 0; i < history_num - 1; i++) {
+        new_history[i] = history[i+1] - history[i];
+    }
+
+    int result = extrapolate(new_history, history_num - 1) + history[history_num - 1];
+    free(new_history);
+    return result;
+}
+
+int extrapolate_backwards(int history[], int history_num) {
+    int zeros = 1;
+    for (int i = 0; i < history_num; i++) {
+        if (history[i] != 0) {
+            zeros = 0;
+            break;
+        }
+    }
+
+    if (zeros) {
+        return 0;
+    }
+
+    int *new_history = (int*)malloc((history_num - 1) * sizeof(int));
+
+    for (int i = 0; i < history_num - 1; i++) {
+        new_history[i] = history[i+1] - history[i];
+    }
+
+    int result = history[0] - extrapolate_backwards(new_history, history_num - 1);
+    free(new_history);
+    return result;
+}