Day9

day9/c/day9.c

@@ -0,0 +1,112 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define char2i(c) (c - 48)
+#define MAX_DISK_SIZE 1024*1024
+
+int main() {
+    char c;
+
+    uint32_t *disk = calloc(MAX_DISK_SIZE, sizeof(disk[0]));
+    int disk_size = 0;
+    uint32_t file_count = 0;
+    int is_file = 1;
+
+    while ((c = getchar()) != EOF) {
+        int n = char2i(c);
+        uint32_t data = is_file ? file_count++ : UINT32_MAX;
+
+        for (int i = 0; i < n; i++) {
+            disk[disk_size++] = data;
+        }
+
+        is_file = !is_file;
+    }
+
+    // Create copy
+    uint32_t *disk_copy = calloc(disk_size, sizeof(disk_copy[0]));
+    memcpy(disk_copy, disk, disk_size * sizeof(disk[0]));
+
+    int last_empty = 0;
+    int inserted_back = 0;
+    for (;;) {
+        // Find next empty space
+        while (disk_copy[last_empty] != UINT32_MAX && last_empty < disk_size - inserted_back - 1) last_empty++;
+
+        if (last_empty >= disk_size - inserted_back - 1) {
+            break;
+        }
+
+        disk_copy[last_empty] = disk_copy[disk_size - inserted_back - 1];
+        disk_copy[disk_size - inserted_back - 1] = UINT32_MAX;
+        inserted_back++;
+    }
+
+    uint64_t checksum = 0;
+
+    for (int i = 0; i < disk_size; i++) {
+        if (disk_copy[i] != UINT32_MAX) {
+            checksum += disk_copy[i] * i;
+        }
+    }
+
+    free(disk_copy);
+
+    printf("%lu\n", checksum);
+
+    // Part two
+    for (int i = file_count - 1; i >= 0; i--) {
+        // Get file size inefficiently
+        int file_size = 0;
+        int file_begin = 0;
+        for (int j = 0; j < disk_size; j++) {
+            if (disk[j] == i) {
+                if (file_size == 0) {
+                    file_begin = j;
+                }
+                file_size++;
+            }
+        }
+
+        // Find empty space
+        for (int j = 0; j < disk_size; j++) {
+            // We only place files left
+            if (disk[j] == i) {
+                break;
+            }
+
+            if (disk[j] == UINT32_MAX) {
+                // Let's see if we have enough space
+                int fit = 1;
+                for (int k = 0; k < file_size; k++) {
+                    if (disk[j + k] != UINT32_MAX) {
+                        fit = 0;
+                        break;
+                    }
+                }
+
+                if (fit) {
+                    for (int k = 0; k < file_size; k++) {
+                        disk[j + k] = i;
+                        disk[file_begin + k] = UINT32_MAX;
+                    }
+                    break;
+                }
+            }
+        }
+    }
+
+    checksum = 0;
+
+    for (int i = 0; i < disk_size; i++) {
+        if (disk[i] != UINT32_MAX) {
+            checksum += disk[i] * i;
+        }
+    }
+
+    free(disk);
+
+    printf("%lu\n", checksum);
+}

day9/sample.txt

@@ -0,0 +1 @@
+2333133121414131402