From eafb73cfc186d3984b23da7e9b01b365cf2543ee Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Mon, 7 Dec 2020 21:11:05 -0800
Subject: [PATCH] Add day 8 solution.

---
 day8.cr | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 day8.cr

diff --git a/day8.cr b/day8.cr
new file mode 100644
index 0000000..f7891f0
--- /dev/null
+++ b/day8.cr
@@ -0,0 +1,84 @@
+require "advent"
+INPUT = input(2020, 8).lines
+
+def part1
+  acc = 0
+  pc = 0
+  visited = Set(Int32).new
+  input = INPUT.clone.map do |s|
+    code, int = s.split(" ")
+    {code, int.to_i32}
+  end
+
+  loop do
+    if visited.includes? pc
+      break
+    end
+    visited << pc
+    code, int = input[pc]
+    case input[pc][0]
+    when "acc"
+      acc += int
+      pc += 1
+    when "jmp"
+      pc += int
+    when "nop"
+      pc += 1
+    end
+  end
+end
+
+def run(prog)
+  acc = 0
+  pc = 0
+  visited = Set(Int32).new
+  loop do
+    if visited.includes? pc
+      return false
+    end
+    return acc if pc >= prog.size
+    visited << pc
+    code, int = prog[pc]
+    case prog[pc][0]
+    when "acc"
+      acc += int
+      pc += 1
+    when "jmp"
+      pc += int
+    when "nop"
+      pc += 1
+    end
+  end
+end
+
+def part2
+  input = INPUT.clone.map do |s|
+    code, int = s.split(" ")
+    {code, int.to_i32}
+  end
+
+  jnp = [] of Int32
+  input.each_with_index do |e, i|
+    op, int = e
+    jnp << i if op == "jmp" || op == "nop"
+  end
+
+  jnp.each do |i|
+    prog = input.clone
+    if prog[i][0] == "jmp"
+      prog[i] = {"nop", prog[i][1]}
+    else
+      prog[i] = {"jmp", prog[i][1]}
+    end
+
+    case i = run(prog)
+    when Bool
+      next
+    when Int32
+      return i
+    end
+  end
+end
+
+puts part1
+puts part2