2020 day 6

2020/1/day1.lua

@@ -0,0 +1,32 @@
+#!/usr/bin/env lua
+-- I'm feeling lazy.
+local numbers = {}
+
+for line in io.lines() do
+    table.insert(numbers, tonumber(line))
+end
+
+local function part1()
+    for _, x in ipairs(numbers) do
+        for _, y in ipairs(numbers) do
+            if x + y == 2020 then
+                return x * y
+            end
+        end
+    end
+end
+
+local function part2()
+    for _, x in ipairs(numbers) do
+        for _, y in ipairs(numbers) do
+            for _, z in ipairs(numbers) do
+                if x + y + z == 2020 then
+                    return x * y * z
+                end
+            end
+        end
+    end
+end
+
+print(part1())
+print(part2())

2020/2/day2.lua

@@ -0,0 +1,35 @@
+#!/usr/bin/env lua
+
+local data = {}
+
+for line in io.lines() do
+    local password_start, n1, n2, char = select(2, line:find('^(%d+)-(%d+) (%l): '))
+    table.insert(data, {tonumber(n1), tonumber(n2), char, line:sub(password_start + 1)})
+end
+
+local function part1()
+    local count = 0
+    for _, line in ipairs(data) do
+        local min, max, char, password = table.unpack(line)
+        local char_count = select(2, password:gsub(char, ''))
+        if min <= char_count and char_count <= max then
+            count = count + 1
+        end
+    end
+    return count
+end
+
+local function part2()
+    local count = 0
+    for _, line in ipairs(data) do
+        local pos1, pos2, char, password = table.unpack(line)
+        local has1, has2 = password:sub(pos1, pos1) == char, password:sub(pos2, pos2) == char
+        if (has1 or has2) and not (has1 and has2) then
+            count = count + 1
+        end
+    end
+    return count
+end
+
+print(part1())
+print(part2())

2020/3/day3.lua

@@ -0,0 +1,24 @@
+local lines = {}
+
+for line in io.lines() do
+    table.insert(lines, line)
+end
+
+local function count_trees(right, down)
+    right = right or 1
+    down = down or 1
+    local count, iteration = 0, 1
+    for index = 1,#lines,down do
+        local pos = ((iteration - 1) * right) % lines[index]:len() + 1
+        if lines[index]:sub(pos, pos) == "#" then
+            count = count + 1
+        end
+        iteration = iteration + 1
+    end
+    return count
+end
+
+local part1 = count_trees(3)
+local part2 = count_trees() * part1 * count_trees(5) * count_trees(7) * count_trees(1, 2)
+print(part1)
+print(part2)

2020/4/day4.lua

@@ -0,0 +1,79 @@
+#!/usr/bin/env lua
+
+local passports, current = {}, {}
+for line in io.lines() do
+    if line == "" then
+        table.insert(passports, current)
+        current = {}
+    end
+    for name, value in line:gmatch("(%a+):(%g+)") do
+        current[name] = value
+    end
+end
+table.insert(passports, current)
+
+local function validate_byr(val)
+    val = tonumber(val)
+    return val and val >= 1920 and val <= 2002
+end
+
+local function validate_iyr(val)
+    val = tonumber(val)
+    return val and val >= 2010 and val <= 2020
+end
+
+local function validate_eyr(val)
+    val = tonumber(val)
+    return val and val >= 2020 and val <= 2030
+end
+
+local function validate_hgt(val)
+    local suffix = val:sub(-2)
+    val = tonumber(val:sub(1, -3))
+    if not val then return false end
+    if suffix == "cm" then
+        return val >= 150 and val <= 193
+    elseif suffix == "in" then
+        return val >= 59 and val <= 76
+    else return false end
+end
+
+local function validate_hcl(val)
+    return val and val:match("#%x%x%x%x%x")
+end
+
+local function validate_ecl(val)
+    return ({amb=true, blu=true, brn=true, gry=true, grn=true, hzl=true, oth=true})[val]
+end
+
+local function validate_pid(val)
+    return val and val:match("^%d%d%d%d%d%d%d%d%d$")
+end
+
+local required_fields = {
+    byr=validate_byr,
+    iyr=validate_iyr,
+    eyr=validate_eyr,
+    hgt=validate_hgt,
+    hcl=validate_hcl,
+    ecl=validate_ecl,
+    pid=validate_pid,
+}
+
+local function validate(run_checks)
+    local count = 0
+    for _, passport in ipairs(passports) do
+        local ok = 1
+        for field, validator in pairs(required_fields) do
+            if passport[field] == nil or (run_checks and not validator(passport[field])) then
+                ok = 0
+                break
+            end
+        end
+        count = count + ok
+    end
+    return count
+end
+
+print(validate(false))
+print(validate(true))

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

2020/6/day6.lua

@@ -0,0 +1,29 @@
+#!/usr/bin/env lua
+local groups, current = {}, {count=0}
+for line in io.lines() do
+    if line == "" then
+        table.insert(groups, current)
+        current = {count=0}
+    else
+        for char in line:gmatch(".") do
+            current[char] = (current[char] or 0) + 1
+        end
+        current.count = current.count + 1
+    end
+end
+table.insert(groups, current)
+
+local any_count, all_count = 0, 0
+for _, group in ipairs(groups) do
+    for name, question_count in pairs(group) do
+        if name ~= "count" then
+            any_count = any_count + 1
+            if question_count == group.count then
+                all_count = all_count + 1
+            end
+        end
+    end
+end
+
+print(any_count)
+print(all_count)

README.md

@@ -5,13 +5,13 @@ My solutions to the Advent of Code puzzles.
 ## Progress
 
 ```
-   15 16 17 18 19
- 1 ██ ██ ██ ██
- 2 ██ ██ ██ ██
- 3 ██ ██ ██ ██
- 4 ██    ██ ██
- 5 ██    ██ ██
- 6 ██    ██
+   15 16 17 18 19 20
+ 1 ██ ██ ██ ██    ██
+ 2 ██ ██ ██ ██    ██
+ 3 ██ ██ ██ ██    ██
+ 4 ██    ██ ██    ██
+ 5 ██    ██ ██    ██
+ 6 ██    ██       ██
  7 ██    ██
  8 ██    ██
  9 █     ██