Change the name of input files.

common.cr

@@ -0,0 +1,22 @@
+module Enumerable(T)
+  def count_each(others)
+    count_map = {} of T => Int32
+    each do |other|
+      count_map[other] = (count_map[other]? || 0) + 1
+    end
+    return count_map
+  end
+end
+
+class Rectangle
+  def initialize(@x : Int32, @y : Int32, @width : Int32, @height : Int32)
+  end
+
+  def each_coord(&block)
+    (@x...(@x + @width)).each do |x|
+      (@y...(@y + @height)).each do |y|
+        yield x, y
+      end
+    end
+  end
+end

day1.cr

@@ -0,0 +1,20 @@
+changes = File.read("day1_input").split("\n")
+  .select { |it| !it.empty? } 
+  .map(&.to_i)
+
+puts "Final frequency: #{changes.sum}"
+
+count = { 0 => 1 }
+acc = 0
+
+changes.cycle do |i|
+  acc += i
+  old_count = count[acc]? || 0
+  new_count = old_count + 1
+  count[acc] = new_count
+
+  if new_count == 2
+    puts acc
+    exit
+  end
+end

day1_1.cr

@@ -1,4 +0,0 @@
-puts File.read("day1").split("\n")
-  .select { |it| !it.empty? } 
-  .map(&.to_i)
-  .sum

day1_2.cr

@@ -1,19 +0,0 @@
-count = { 0 => 1 }
-acc = 0
-changes = File.read("day1").split("\n")
-  .select { |it| !it.empty? } 
-  .map(&.to_i)
-
-while true
-  changes.each do |i|
-    acc += i
-    old_count = count[acc]? || 0
-    new_count = old_count + 1
-    count[acc] = new_count
-
-    if new_count == 2
-      puts acc
-      exit
-    end
-  end
-end

day2.cr

@@ -0,0 +1,30 @@
+require "./common.cr"
+
+lines = File.read("day2_input").split("\n")
+lines.pop
+
+CHARS = ('a'..'z').to_a
+
+def has_n?(string, n)
+  return string.chars.count_each(CHARS).any?(&.[](1).==(n))
+end
+
+def count_changes(s1, s2)
+  pairs = s1.chars.zip s2.chars
+  total = 0
+  pairs.each do |pair|
+    total += 1 if pair[0] != pair[1]
+  end
+  return total
+end
+
+two = lines.count { |s| has_n?(s, 2) }
+three = lines.count { |s| has_n?(s, 3) }
+puts "\"Hash\": #{two * three}"
+
+lines.product(lines).each do |pair|
+  if count_changes(pair[0], pair[1]) == 1
+    puts "Strings: #{pair[0]}, #{pair[1]}" 
+    exit
+  end
+end

day2_1.cr

@@ -1,15 +0,0 @@
-lines = File.read("day2").split("\n")
-lines.pop
-
-CHARS = ('a'..'z').to_a
-
-def has_n?(string, n)
-  CHARS.each do |c|
-    return true if string.count(c) == n
-  end
-  return false
-end
-
-two = lines.count { |s| has_n?(s, 2) }
-three = lines.count { |s| has_n?(s, 3) }
-puts two * three

day2_2.cr

@@ -1,15 +0,0 @@
-lines = File.read("day2").split("\n")
-lines.pop
-
-def count_changes(s1, s2)
-  pairs = s1.chars.zip s2.chars
-  total = 0
-  pairs.each do |pair|
-    total += 1 if pair[0] != pair[1]
-  end
-  return total
-end
-
-lines.product(lines).each do |pair|
-  puts "#{pair[0]}, #{pair[1]}" if count_changes(pair[0], pair[1]) == 1
-end

day3.cr

@@ -0,0 +1,38 @@
+require "./common.cr"
+
+lines = File.read("day3_input").split("\n")
+lines.pop
+
+REGEX = /#([0-9]+) @ ([0-9]+),([0-9]+): ([0-9]+)x([0-9]+)/
+
+claims = {} of Int32 => Rectangle
+lines.each do |line|
+  match = line.match(REGEX).not_nil!
+  claim = match[1].to_i32
+  x = match[2].to_i32
+  y = match[3].to_i32
+  width = match[4].to_i32
+  height = match[5].to_i32
+  claims[claim] = Rectangle.new(x, y, width, height)
+end
+
+claimed_coords = {} of Tuple(Int32, Int32) => Int32
+claims.values.each do |claim|
+  claim.each_coord do |x, y|
+    coord = {x, y}
+    claimed_coords[coord] = (claimed_coords[coord]? || 0) + 1
+  end
+end
+
+puts "Overlapping: #{claimed_coords.values.count &.>(1)}"
+
+claims.each do |k, v|
+  count_overlapped = 0
+  v.each_coord do |x, y|
+    count_overlapped += 1 if claimed_coords[{x, y}] > 1
+  end
+  if count_overlapped == 0
+    puts "No overlaps: #{k}"
+    exit
+  end
+end