From f2204e554bf8b1fa7fdfa2a19ccc867d8f3756a8 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Thu, 4 Dec 2025 09:29:39 +0100
Subject: [PATCH] Moderately cursed 2025 day 4 part 1

---
 2025/day04/README.md  | 11 ++++++++++
 2025/day04/sample.txt | 10 +++++++++
 2025/day04/solve.sql  | 47 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+)
 create mode 100644 2025/day04/README.md
 create mode 100644 2025/day04/sample.txt
 create mode 100644 2025/day04/solve.sql

diff --git a/2025/day04/README.md b/2025/day04/README.md
new file mode 100644
index 0000000..a3979df
--- /dev/null
+++ b/2025/day04/README.md
@@ -0,0 +1,11 @@
+# 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
+```
diff --git a/2025/day04/sample.txt b/2025/day04/sample.txt
new file mode 100644
index 0000000..8209399
--- /dev/null
+++ b/2025/day04/sample.txt
@@ -0,0 +1,10 @@
+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.
diff --git a/2025/day04/solve.sql b/2025/day04/solve.sql
new file mode 100644
index 0000000..b4bf4cc
--- /dev/null
+++ b/2025/day04/solve.sql
@@ -0,0 +1,47 @@
+-- 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;