From 22cfef91fd8c3c6deee374a2c3dbad63eb8d6ce1 Mon Sep 17 00:00:00 2001
From: Benno Lorenz <benno.lorenz@rsp-germany.com>
Date: Wed, 3 Dec 2025 15:47:37 +0100
Subject: [PATCH 1/2] day 2

---
 src/days/day2.zig | 74 +++++++++++++++++++++++++++++++++++++++++++++++
 src/main.zig      |  7 +++++
 2 files changed, 81 insertions(+)
 create mode 100644 src/days/day2.zig

diff --git a/src/days/day2.zig b/src/days/day2.zig
new file mode 100644
index 0000000..b1c4711
--- /dev/null
+++ b/src/days/day2.zig
@@ -0,0 +1,74 @@
+const std = @import("std");
+
+pub fn day2pt1(ranges: []const u8) !usize {
+    var i = std.mem.splitScalar(u8, ranges, ',');
+    var sum: usize = 0;
+    while (i.next()) |range| {
+        var j = std.mem.splitScalar(u8, range, '-');
+        const range_start = try std.fmt.parseInt(usize, j.next().?, 10);
+        const range_end = try std.fmt.parseInt(usize, j.next().?, 10);
+
+        var k = range_start;
+        const max_len = 32;
+        var buf: [max_len]u8 = undefined;
+        while (k <= range_end) {
+            const current_id = try std.fmt.bufPrint(&buf, "{d}", .{k});
+            if (current_id.len % 2 == 0) {
+                const half = current_id.len / 2;
+                if (std.mem.eql(u8, current_id[0..half], current_id[half..current_id.len])) {
+                    sum += k;
+                }
+            }
+            k += 1;
+        }
+    }
+    return sum;
+}
+
+pub fn day2pt2(ranges: []const u8) !usize {
+    var i = std.mem.splitScalar(u8, ranges, ',');
+    var sum: usize = 0;
+    while (i.next()) |range| {
+        var j = std.mem.splitScalar(u8, range, '-');
+        const range_start = try std.fmt.parseInt(usize, j.next().?, 10);
+        const range_end = try std.fmt.parseInt(usize, j.next().?, 10);
+
+        var k = range_start;
+        const max_len = 32;
+        var buf: [max_len]u8 = undefined;
+        while (k <= range_end) {
+            const current_id = try std.fmt.bufPrint(&buf, "{d}", .{k});
+            const len = current_id.len;
+            var found = false;
+            // Try all possible substring lengths that divide the length - should be made more efficient （＞人＜；）
+            for (1..len / 2 + 1) |sub_len| {
+                if (len % sub_len != 0) continue;
+                const repeats = len / sub_len;
+                if (repeats < 2) continue;
+                const sub = current_id[0..sub_len];
+                var valid = true;
+                for (1..repeats) |r| {
+                    if (!std.mem.eql(u8, sub, current_id[r * sub_len .. (r + 1) * sub_len])) {
+                        valid = false;
+                        break;
+                    }
+                }
+                if (valid) {
+                    found = true;
+                    break;
+                }
+            }
+            if (found) {
+                sum += k;
+            }
+            k += 1;
+        }
+    }
+    return sum;
+}
+
+test "Day 2 example testing" {
+    const example_input = "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124";
+    try std.testing.expectEqual(try day2pt1(example_input), 1227775554);
+    try std.testing.expectEqual(try day2pt2(example_input), 4174379265);
+}
diff --git a/src/main.zig b/src/main.zig
index 594ce17..76411ed 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const loadpuzzle = @import("utils/loadpuzzle.zig");
 const day1 = @import("days/day1.zig");
+const day2 = @import("days/day2.zig");
 
 pub fn main() !void {
     // Prints to stderr, ignoring potential errors.
@@ -12,6 +13,12 @@ pub fn main() !void {
     const day1_input = try loadpuzzle.readFile(gpa, "puzzle_input/day1.txt");
     std.debug.print("Day 1 Part 1: {any}\n", .{try day1.day1pt1(day1_input)});
     std.debug.print("Day 1 Part 2: {any}\n", .{try day1.day1pt2(day1_input)});
+    gpa.free(day1_input);
+
+    const day2_input = try loadpuzzle.readFile(gpa, "puzzle_input/day2.txt");
+    std.debug.print("Day 2 Part 1: {any}\n", .{try day2.day2pt1(day2_input)});
+    std.debug.print("Day 2 Part 1: {any}\n", .{try day2.day2pt2(day2_input)});
+    gpa.free(day2_input);
 }
 
 test "simple test" {

From 519948d83fd2427dbc88340df203316c3f989087 Mon Sep 17 00:00:00 2001
From: Benno Lorenz <benno.lorenz@rsp-germany.com>
Date: Wed, 3 Dec 2025 15:47:53 +0100
Subject: [PATCH 2/2] day 2 input

---
 puzzle_input/day2.txt | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 puzzle_input/day2.txt

diff --git a/puzzle_input/day2.txt b/puzzle_input/day2.txt
new file mode 100644
index 0000000..5531ea6
--- /dev/null
+++ b/puzzle_input/day2.txt
@@ -0,0 +1 @@
+16100064-16192119,2117697596-2117933551,1-21,9999936269-10000072423,1770-2452,389429-427594,46633-66991,877764826-877930156,880869-991984,18943-26512,7216-9427,825-1162,581490-647864,2736-3909,39327886-39455605,430759-454012,1178-1741,219779-244138,77641-97923,1975994465-1976192503,3486612-3602532,277-378,418-690,74704280-74781349,3915-5717,665312-740273,69386294-69487574,2176846-2268755,26-45,372340114-372408052,7996502103-7996658803,7762107-7787125,48-64,4432420-4462711,130854-178173,87-115,244511-360206,69-86
\ No newline at end of file