From 2543ec7db39771d6bca1083988ff869e83aba2be Mon Sep 17 00:00:00 2001
From: Lucidiot <lucidiot@protonmail.com>
Date: Mon, 7 Dec 2020 01:39:26 +0100
Subject: [PATCH] 2020 day 3

---
 2020/3/day3.lua | 24 ++++++++++++++++++++++++
 README.md       |  2 +-
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 2020/3/day3.lua

diff --git a/2020/3/day3.lua b/2020/3/day3.lua
new file mode 100644
index 0000000..84104bc
--- /dev/null
+++ b/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)
diff --git a/README.md b/README.md
index 158d37a..48283a3 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ My solutions to the Advent of Code puzzles.
    15 16 17 18 19 20
  1 ██ ██ ██ ██    ██
  2 ██ ██ ██ ██    ██
- 3 ██ ██ ██ ██
+ 3 ██ ██ ██ ██    ██
  4 ██    ██ ██
  5 ██    ██ ██
  6 ██    ██