2025 day 2

ruby/2025/2/bin/problem

@@ -0,0 +1,7 @@
+#!/usr/bin/env ruby
+
+require "id_range"
+
+id_ranges = STDIN.read.chomp.split(",").map{ |chunk| IdRange.for chunk }
+puts "Part 1: #{id_ranges.map(&:invalid_ids).flatten.sum}"
+puts "Part 2: #{id_ranges.map(&:silly_invalid_ids).flatten.sum}"

ruby/2025/2/lib/id_range.rb

@@ -0,0 +1,41 @@
+class Integer
+  def invalid_id?
+    string = to_s
+    return false if string.length.odd?
+    
+    string[..((string.length / 2) - 1)] == string[(string.length / 2)..]
+  end
+
+  def silly_invalid_id?
+    string = to_s
+    for pattern_length in 1.upto(string.length - 1)
+      next if string.length % pattern_length != 0
+
+      pattern = string[0..(pattern_length - 1)]
+      rest = string[pattern_length..]
+      return true if rest.gsub(pattern, "").empty?
+    end
+
+    false
+  end
+end
+
+class IdRange
+  attr_reader :range
+  def initialize(range)
+    @range = range
+  end
+
+  def self.for(chunk)
+    low, high = chunk.split("-").map(&:to_i)
+    new low..high
+  end
+
+  def invalid_ids
+    range.select(&:invalid_id?)
+  end
+
+  def silly_invalid_ids
+    range.select(&:silly_invalid_id?)
+  end
+end

ruby/2025/2/test/test_id_range.rb

@@ -0,0 +1,29 @@
+require "minitest/autorun"
+require "id_range"
+
+class TestIdRange < Minitest::Test
+  def test_invalid_ids
+    assert_equal([11, 22], IdRange.for("11-22").invalid_ids)
+    assert_equal([99], IdRange.for("95-115").invalid_ids)
+    assert_equal([1188511885], IdRange.for("1188511880-1188511890").invalid_ids)
+    assert_equal([222222], IdRange.for("222220-222224").invalid_ids)
+    assert_equal([], IdRange.for("1698522-1698528").invalid_ids)
+    assert_equal([446446], IdRange.for("446443-446449").invalid_ids)
+    assert_equal([38593859], IdRange.for("38593856-38593862").invalid_ids)
+  end
+
+  def test_silly_invalid_ids
+    assert_equal([11, 22], IdRange.for("11-22").silly_invalid_ids)
+    assert_equal([99, 111], IdRange.for("95-115").silly_invalid_ids)
+    assert_equal([999, 1010], IdRange.for("998-1012").silly_invalid_ids)
+    assert_equal([1188511885], IdRange.for("1188511880-1188511890").silly_invalid_ids)
+    assert_equal([222222], IdRange.for("222220-222224").silly_invalid_ids)
+    assert_equal([], IdRange.for("1698522-1698528").silly_invalid_ids)
+    assert_equal([446446], IdRange.for("446443-446449").silly_invalid_ids)
+    assert_equal([38593859], IdRange.for("38593856-38593862").silly_invalid_ids)
+
+    assert_equal([565656], IdRange.for("565653-565659").silly_invalid_ids)
+    assert_equal([824824824], IdRange.for("824824821-824824827").silly_invalid_ids)
+    assert_equal([2121212121], IdRange.for("2121212118-2121212124").silly_invalid_ids)
+  end
+end