Day 2: Part 2

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)

day2/day2_part2.lua

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+--Lua 5.4.2
+local File = io.open("input.txt", "r")
+
+if not File then
+    print("File not found")
+    return
+end
+
+local function IsReportSafe(Numbers)
+    local IsSafe = true
+    local LastSign = 0
+    local LastNumber
+    for _, Number in next, Numbers 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
+    return IsSafe
+end
+
+local function Clone(t) --surface level copy
+    local Cloned = {}
+    for Key, Value in next, t do
+        Cloned[Key] = Value
+    end
+    return Cloned
+end
+
+local SafeReports = 0
+
+for Line in File:lines() do
+    local Numbers = {}
+    for Number in Line:gmatch("%d+") do
+        table.insert(Numbers, tonumber(Number))
+    end
+    if IsReportSafe(Numbers) then
+        SafeReports = SafeReports + 1
+    else
+        for Index = 1, #Numbers do
+            local NumbersCopy = Clone(Numbers) --yikes
+            table.remove(NumbersCopy, Index)
+            if IsReportSafe(NumbersCopy) then
+                SafeReports = SafeReports + 1
+                break
+            end
+        end
+    end
+end
+
+print("Safe reports:", SafeReports)