c 2024 day 9

c/2024/9/disk_fragmenter.c

@@ -0,0 +1,101 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include "../../lib/aoc.h"
+
+#define EMPTY -1
+
+typedef struct File {
+  int id;
+  int *location;
+  int size;
+  bool free;
+} File;
+
+int main() {
+  char *input = aoc_read_input();
+  int input_size = strlen(input);
+
+  int disk[200000];
+  int *write_head = disk;
+  int file_number = 0;
+  int total_file_size = 0;
+
+  File files[10000];
+  int files_count = 0;
+  File empties[10000];
+  int empties_count = 0;
+
+  int i = 0;
+  while (i < input_size) {
+    int file_size = input[i++] - '0';
+    total_file_size += file_size;
+
+    files[files_count].id = file_number;
+    files[files_count].location = write_head;
+    files[files_count].size = file_size;
+    files_count++;
+      
+    for (int j = 0; j < file_size; j++) {
+      *write_head = file_number;
+      write_head++;
+    }
+    file_number++;
+
+    int empty_size = input[i++] - '0';
+    if (empty_size > 0) {
+      empties[empties_count].id = EMPTY;
+      empties[empties_count].location = write_head;
+      empties[empties_count].size = empty_size;
+      empties_count++;
+    }
+
+    for (int j = 0; j < empty_size; j++) {
+      *write_head = EMPTY;
+      write_head++;
+    }
+  }
+
+  int *read_head = write_head - 1;
+  write_head = disk;
+
+  while (read_head > write_head) {
+    if (*read_head == EMPTY) read_head--;
+    else if (*write_head != EMPTY) write_head++;
+    else {
+      *write_head = *read_head;
+      *read_head = EMPTY;
+    }
+  }
+
+  long checksum = 0l;
+  for (int i = 0; i < total_file_size; i++) checksum += i * disk[i];
+
+  for (int i = files_count - 1; i >= 0; i--) {
+    for (int j = 0; j < empties_count; j++) {
+      if (empties[j].size >= files[i].size) {
+	files[i].location = empties[j].location;
+	empties[j].size -= files[i].size;
+	empties[j].location += files[i].size;
+	break;
+      }
+      if (empties[j].location > files[i].location) break;
+    }
+  }
+
+  long second_checksum = 0l;
+  for (int i = 0; i < files_count; i++) {
+    for (int j = 0; j < files[i].size; j++) {
+      second_checksum += (files[i].id * (files[i].location - disk + j));
+    }
+  }
+
+
+  printf("Part 1: %ld\n", checksum);
+  printf("Part 2: %ld\n", second_checksum);
+  
+  aoc_free();
+  return 0;
+}