1 files changed, 72 insertions, 0 deletions
diff --git a/2.lua b/2.lua
new file mode 100644
index 0000000..f8068ef
--- /dev/null
+++ b/2.lua
@@ -0,0 +1,72 @@
+local function is_safe(a)
+  local up = false
+  local down = false
+  local prev = nil
+
+  for i, number in ipairs(a) do
+    number = tonumber(number)
+
+    if prev == nil then
+      prev = number
+      goto continue
+    end
+
+    if down==false and up==false then
+      if number < prev then down = true
+      elseif number > prev then up = true
+      else return false end
+    end
+
+    if up then
+      if prev > number then return false end
+      local r=number-prev
+      if r~=1 and r~=2 and r~= 3 then return false end
+      prev = number
+    end
+
+    if down then
+      if number > prev then return false end
+      local r=prev-number
+      if r~=1 and r~=2 and r~= 3 then return false end
+      prev = number
+    end
+
+  ::continue::
+  end
+  return true
+end
+
+local file = io.open("2-input.txt", "r")
+
+local safe = 0
+local safe_one_skip = 0
+
+for line in file:lines() do
+  local numbers = line:gmatch("[^%s]+")
+  local numbers_arr = {}
+  for i in numbers do
+    table.insert(numbers_arr, i)
+  end
+
+  if is_safe(numbers_arr) then
+    safe = safe + 1
+    safe_one_skip = safe_one_skip + 1
+  else
+    for i=1, #numbers_arr do
+      local n = table.remove(numbers_arr, i)
+      if is_safe(numbers_arr) then
+        safe_one_skip = safe_one_skip + 1
+        break
+      end
+      table.insert(numbers_arr, i, n)
+    end
+  end
+
+end
+
+file:close()
+print("puzzle 1:", safe)
+print("puzzle 2:", safe_one_skip)
+
+-- 490
+-- 536