2020 day 5

2020/5/day5.lua

@@ -0,0 +1,28 @@
+#!/usr/bin/env lua
+local seat_ids = {}
+
+local function parse(line)
+    local word = tonumber(line:gsub("[FBLR]", {F="0", B="1", L="0", R="1"}), 2)
+    local row, column = word >> 3, word & 7
+    return row * 8 + column
+end
+
+for line in io.lines() do
+   table.insert(seat_ids, parse(line))
+end
+
+local lowest_id, highest_id = math.min(table.unpack(seat_ids)), math.max(table.unpack(seat_ids))
+print(highest_id)
+
+-- Build an equivalent of a set for faster access
+local seat_ids_set = {}
+for _, id in ipairs(seat_ids) do
+    seat_ids_set[id] = true
+end
+
+for id = lowest_id, highest_id do
+    if not seat_ids_set[id] and seat_ids_set[id - 1] and seat_ids_set[id + 1] then
+        print(id)
+        return
+    end
+end

README.md

@@ -10,7 +10,7 @@ My solutions to the Advent of Code puzzles.
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