Day 2: Part 1

day2/day2_part1.lua

@@ -0,0 +1,42 @@
+--Lua 5.4.2
+local File = io.open("input.txt", "r")
+
+if not File then
+    print("File not found")
+    return
+end
+
+local SafeReports = 0
+
+for Line in File:lines() do
+    local IsSafe = true
+    local LastSign = 0
+    local LastNumber
+    for Number in Line:gmatch("%d+") do
+        if not LastNumber then
+            LastNumber = Number
+            goto continue
+        end
+        local Difference = math.abs(Number - LastNumber)
+        if Difference > 3 or Difference == 0 then
+            IsSafe = false
+            break
+        end
+        local Sign = (Number - LastNumber) > 0 and 1 or -1
+        if LastSign == 0 then
+            LastSign = Sign
+        else
+            if Sign ~= LastSign then
+                IsSafe = false
+                break
+            end
+        end
+        LastNumber = Number
+        ::continue::
+    end
+    if IsSafe then
+        SafeReports = SafeReports + 1
+    end
+end
+
+print("Safe reports:", SafeReports)