4 files changed, 178 insertions(+), 0 deletions(-)

A 2023/11.lua
A 2023/11.pdf
A 2023/11.tex
A 2023/11.txt

@@ 0,0 1,20 @@
+local xs, ys, y, G = {}, {}, 1, string.byte'#'
+for line in io.lines() do
+	for x = 1, #line do
+		if string.byte(line, x) == G then
+			xs[#xs + 1] = x
+			ys[#ys + 1] = y
+		end
+	end
+	y = y + 1
+end
+table.sort(xs)
+
+local ans, off, oldx, oldy = 0, 0, math.huge, math.huge
+for i, x in ipairs(xs) do
+	local y, n = ys[i], 2*i - #xs - 1
+	off = off + (i-1) * (i-n) * (math.max(x-oldx-1, 0) + math.max(y-oldy-1, 0))
+	ans = ans + n * (x+y)
+	oldx, oldy = x, y
+end
+print(ans + off, ans + off*999999)

@@ 0,0 1,18 @@
+\documentclass{article}
+\usepackage{amsmath}
+\usepackage[letterpaper]{geometry}
+
+\title{Advent of Code 2023 - Day 11}
+\date{}
+
+\begin{document}
+
+\maketitle
+
+Given the number of galaxies $n$, expansion scale $k$, sorted $x$ coordinates $x_1$, ..., $x_n$, and sorted $y$ coordinates $y_1$, ..., $y_n$, the sum of the distances between each galaxy, accounting for expansion, is
+
+\begin{equation*}
+\sum_{i=1}^{n} (2i-n-1)(x_i + y_i) + (k-1)(i-1)(n-i+1)(\textup{max}(x_i - x_{i-1} - 1, 0) + \textup{max}(y_i - y_{i-1} - 1, 0)))
+\end{equation*}
+
+\end{document}

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