day 09

aoc/aoc.h

@@ -57,6 +57,12 @@ typedef double f64;
 #define Megabytes(x) ((u64) (x) << 20)
 #define Gigabytes(x) ((u64) (x) << 30)
 
+#define DYNAMIC_ARRAY(type) \
+    struct { \
+        type *data; \
+        isize len, cap; \
+    }
+
 #define push(slice, arena) \
     ((slice)->len >= ((slice)->cap) \
      ? grow(slice, sizeof(*(slice)->data), arena), \

aoc/common.h

@@ -134,7 +134,7 @@ vec2_sub(Vec2 a, Vec2 b) {
 
 static inline Vec2
 vec2(f32 x, f32 y) {
-    Vec2 result = { x, y };
+    Vec2 result = {{ x, y }};
     return result;
 }
 

day-09/main.c

@@ -0,0 +1,121 @@
+#include "aoc.h"
+
+typedef struct {
+    int id; // -1 if free space
+    int len;
+    int offset;
+} Block;
+
+static void
+dump(int *ids, int len) {
+    for (int i = 0; i < len; i++) {
+        if (ids[i] == -1) {
+            printf(".");
+        }
+        else {
+            printf("%d", ids[i] % 10);
+        }
+    }
+    puts("");
+}
+
+static void
+disk_from_blocks(i32 *disk, Block *blocks, usize block_count) {
+    for (usize i = 0; i < block_count; i++) {
+        Block *block = blocks + i;
+        for (int j = 0; j < block->len; j++) {
+            disk[j] = block->id;
+        }
+        disk += block->len;
+    }
+}
+
+int main(int argc, char **argv) {
+    (void) argc;
+    Arena *arena = make_arena(Megabytes(10));
+    str input = str_trim(read_file(arena, argv[1]));
+
+    enum {
+        STATE_BLOCK,
+        STATE_SPACE,
+    } state = STATE_BLOCK;
+    int block_id = 0;
+
+    DYNAMIC_ARRAY(Block) blocks = {0};
+
+    isize total_size = 0;
+    for (usize i = 0; i < input.len; ++i) {
+        int len = input.data[i] - '0';
+        *push(&blocks, arena) = (Block) {
+            .id = (state == STATE_BLOCK) ? block_id : -1, 
+            .len = len, 
+            .offset = total_size
+        };
+        total_size += len;
+        if (state == STATE_BLOCK) {
+            block_id++;
+            state = STATE_SPACE;
+        }
+        else {
+            state = STATE_BLOCK;
+        }
+    }
+    ASSERT(state == STATE_SPACE);
+
+    i32 *disk = ARENA_ALLOC_ARRAY(arena, i32, total_size);
+    disk_from_blocks(disk, blocks.data, blocks.len);
+
+    isize to = 0, from = total_size - 1;
+    for (;;) {
+        while (to <= from && disk[to] != -1) {
+            to++;
+        }
+        while (from > to && disk[from] == -1) {
+            from--;
+        }
+        if (to >= from) {
+            break;
+        }
+        ASSERT((disk[to] == -1) && (disk[from] != -1));
+        disk[to] = disk[from];
+        disk[from] = -1;
+        from--;
+        to++;
+    }
+
+    i64 part_1 = 0;
+    for (isize i = 0; i < total_size && disk[i] != -1; i++) {
+        part_1 += i * disk[i];
+    }
+    printf("%ld\n", part_1);
+
+    // restore original layout
+    disk_from_blocks(disk, blocks.data, blocks.len);
+
+    for (isize from_block_index = blocks.len - 1; from_block_index >= 0; from_block_index -= 2) {
+        Block *from = blocks.data + from_block_index;
+        ASSERT(from->id != -1);
+
+        for (isize to_block_index = 1; to_block_index < from_block_index; to_block_index += 2) {
+            Block *to = blocks.data + to_block_index;
+            ASSERT(to->id == -1);
+            if (from->len <= to->len) {
+                for (isize i = 0; i < from->len; i++) {
+                    disk[to->offset + i] = from->id;
+                    disk[from->offset + i] = -1;
+                }
+                to->offset += from->len;
+                to->len -= from->len;
+                break;
+            }
+        }
+    }
+
+    i64 part_2 = 0;
+    for (isize i = 0; i < total_size; i++) {
+        if (disk[i] != -1) {
+            part_2 += i * disk[i];
+        }
+    }
+    printf("%ld\n", part_2);
+}

day-09/test.txt

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

day-09/test2.txt

@@ -0,0 +1 @@
+233313312141413140223331331214141314022333133121414131402