From 516e6ed4a9066fa43d6159b2a0ec58416ab28013 Mon Sep 17 00:00:00 2001
From: xander <xander@biltopia.org>
Date: Sun, 7 Dec 2025 13:12:06 +0100
Subject: solve up to day 7

---
 src/day02.zig | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 src/day02.zig

(limited to 'src/day02.zig')

diff --git a/src/day02.zig b/src/day02.zig
new file mode 100644
index 0000000..f764589
--- /dev/null
+++ b/src/day02.zig
@@ -0,0 +1,78 @@
+const std = @import("std");
+const print = std.debug.print;
+
+pub fn solve(part: []u8, reader: *std.Io.Reader, _: std.mem.Allocator) !void {
+    if (std.mem.eql(u8, part, "1")) {
+        try part1(reader);
+    } else {
+        try part2(reader);
+    }
+}
+
+fn digits(number: usize) usize {
+    var value = number;
+    var n: usize = 0;
+    while (value != 0) : (value /= 10) {
+        n += 1;
+    }
+    return n;
+}
+
+fn part1(reader: *std.Io.Reader) !void {
+    var output: usize = 0;
+    while (reader.takeDelimiter(',')) |line| {
+        const trimmed = std.mem.trimRight(u8, line.?, &[_]u8{'\n'});
+        if (trimmed.len == 0) break;
+        var split = std.mem.splitScalar(u8, trimmed, '-');
+        var start = try std.fmt.parseInt(usize, split.next().?, 10);
+        const end = try std.fmt.parseInt(usize, split.next().?, 10);
+        while (start <= end): (start += 1) {
+            const n = digits(start);
+            if (n % 2 == 0 and start % std.math.pow(usize, 10,n/2) == start / std.math.pow(usize, 10,n/2)) {
+                output += start;
+                start += std.math.pow(usize, 2,n/2);
+            }
+        }
+
+    } else |_| {
+    }
+    print("{d}\n", .{output});
+}
+
+fn part2(reader: *std.Io.Reader) !void {
+    var output: usize = 0;
+    while (reader.takeDelimiter(',')) |line| {
+        const trimmed = std.mem.trimRight(u8, line.?, &[_]u8{'\n'});
+        if (trimmed.len == 0) break;
+        var split = std.mem.splitScalar(u8, trimmed, '-');
+        var start = try std.fmt.parseInt(usize, split.next().?, 10);
+        const end = try std.fmt.parseInt(usize, split.next().?, 10);
+        while (start <= end): (start += 1) {
+            const n = digits(start);
+            for (1..n) |i| {
+                if (n % i == 0) {
+                    const p: usize = std.math.pow(usize, 10,i);
+                    if (start % p != 0) {
+                        const div = start / (start % p);
+                        var c: usize = 0;
+
+                        for (0..n/i - 1) |_| {
+                            c *= p;
+                            c += p;
+                        }
+                        c += 1;
+
+                        if (div == c){
+                            output += start;
+                            start += std.math.pow(usize, 2, n/2);
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+
+    } else |_| {
+    }
+    print("{d}\n", .{output});
+}
-- 
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