From 7757fd2b498f7aa59a0756a38c7c553fe3902219 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Sat, 12 Dec 2020 22:09:28 -0800
Subject: [PATCH] Add day 13 solution.

---
 day13.cr | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 day13.cr

diff --git a/day13.cr b/day13.cr
new file mode 100644
index 0000000..fbc29e5
--- /dev/null
+++ b/day13.cr
@@ -0,0 +1,34 @@
+require "advent"
+INPU = input(2020, 13).lines
+INPUT = {INPU[0].to_i32, INPU[1].split(",")}
+
+def part1(input)
+  early, busses = input
+  busses.reject! &.==("x")
+  busses = busses.map &.to_i32
+  bbus = busses.min_by do |b|
+    (early / b).ceil * b
+  end
+  diff = bbus * (((early/bbus).ceil * bbus).to_i32 - early)
+end
+
+def part2(input)
+  _, busses = input
+  busses = busses.map_with_index do |x, i|
+    x.to_i32?.try { |n| { n, i } }
+  end
+  busses = busses.compact
+  n = 0_i64
+  iter = 1_i64
+  busses.each do |m, i|
+    while (n + i) % m != 0
+      n += iter
+    end
+    iter *= m
+  end
+  puts n
+  puts busses
+end
+
+puts part1(INPUT.clone)
+puts part2(INPUT.clone)