Day 02

1 files changed, 70 insertions, 0 deletions

diff --git a/02.lua b/02.lua
new file mode 100644
index 0000000..ce28bb6
--- /dev/null
+++ b/02.lua
@@ -0,0 +1,70 @@
+local Report = {}
+Report.__index = Report
+
+function Report:new (values)
+    if #values == 0 then error "Cannot construct an empty report." end
+    setmetatable(values, Report)
+    return values
+end
+
+local function valid_jump (start, finish)
+    local diff = finish - start
+    return diff >= 1 and diff <= 3
+end
+
+function Report:is_safe_factor (mult, allow_dampen)
+    local prev = self[1] * mult
+    for i = 2,#self do
+        local cur = self[i] * mult
+
+        if valid_jump(prev, cur) then
+            prev = cur
+        elseif not allow_dampen then
+            return false
+        else
+            local remove_cur = i == #self or valid_jump(prev, self[i+1] * mult)
+
+            if not remove_cur then
+                local remove_prev = i == 2 or valid_jump(self[i-2] * mult, cur)
+                if not remove_prev then return false end
+                prev = cur
+            end
+
+            allow_dampen = false
+        end
+    end
+    return true
+end
+
+function Report:is_safe (allow_dampen)
+    return self:is_safe_factor(1, allow_dampen) or
+        self:is_safe_factor(-1, allow_dampen)
+end
+
+local input = {}
+
+for line in function () return io.read("*l") end do
+    local parsed = {}
+    for v in line:gmatch("%d+") do
+        table.insert(parsed, tonumber(v))
+    end
+    table.insert(input, Report:new(parsed))
+end
+
+function input:sum_safe (allow_dampen)
+    local sum = 0
+    for _, x in ipairs(input) do
+        if x:is_safe(allow_dampen) then sum = sum + 1 end
+    end
+    return sum
+end
+
+function input:part1 ()
+    print(self:sum_safe(false))
+end
+
+function input:part2 ()
+    print(self:sum_safe(true))
+end
+
+return input