Moderately cursed 2025 day 4 part 1

2025/day04/README.md

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+# Day 04: SQLite sql
+
+Did you know SQLite does not have procedural extensions? I did not when I started this. Regardless,
+to run:
+
+```console
+$ sqlite3 < solve.sql
+part1
+-----
+13
+```

2025/day04/sample.txt

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+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.

2025/day04/solve.sql

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+-- First import raw data into a table so we can work
+CREATE TABLE raw_data(line_data VARCHAR NOT NULL);
+.import --csv './sample.txt' raw_data
+-- Then use the auto-incrementing ID to add a y coordinate
+CREATE TABLE grid_lines(
+    y INTEGER PRIMARY KEY,
+    line_data VARCHAR NOT NULL
+);
+INSERT INTO grid_lines(line_data)
+SELECT line_data
+FROM raw_data;
+-- Now create a table to hold the paper rolls
+CREATE TABLE rolls(
+    x INTEGER NOT NULL,
+    y INTEGER NOT NULL,
+    PRIMARY KEY (x, y)
+);
+WITH RECURSIVE cte AS (
+    SELECT y,
+        1 x,
+        line_data,
+        substr(line_data, 1, 1) c
+    FROM grid_lines
+    UNION ALL
+    SELECT y,
+        x + 1,
+        line_data,
+        substr(line_data, x + 1, 1)
+    FROM cte
+    WHERE x <= length(line_data)
+)
+INSERT INTO rolls
+SELECT x,
+    y
+FROM cte
+WHERE c = '@';
+-- Now compute part 1
+SELECT COUNT(*) as part1
+FROM rolls r
+WHERE (
+        SELECT COUNT(*) - 1
+        FROM rolls o
+        WHERE o.x >= r.x - 1
+            AND o.x <= r.x + 1
+            AND o.y >= r.y - 1
+            AND o.y <= r.y + 1
+    ) < 4;