2 files changed, 74 insertions(+), 0 deletions(-)

A day05/day05.lua
A day05/day05.test

@@ 0,0 1,65 @@
+#! /usr/bin/env lua
+--
+-- day05.lua
+-- Copyright (C) 2022 Adrian Perez de Castro <aperez@igalia.com>
+--
+-- Distributed under terms of the MIT license.
+--
+
+-- Contains the lines of input describing the initial contents of the
+-- stacks, to be parsed *after* knowing how many stacks are there.
+local stacks_lines = {}
+
+while true do
+   local line = io.read()
+   if line == "" then
+      break
+   end
+
+   stacks_lines[#stacks_lines+1] = line
+end
+
+-- Last read line contains the numbered stacks, the last number will be
+-- the same as the amount of stacks being handled. Also remove that last
+-- line from the pending-to-parse input.
+local nstacks = 0
+for n in stacks_lines[#stacks_lines]:gmatch("%s*(%d+)%s*") do
+   nstacks = tonumber(n)
+end
+table.remove(stacks_lines)
+
+-- Table where each element is a stack, initially empty.
+local stacks = {}
+for i = 1, nstacks do
+   stacks[i] = {}
+end
+
+-- Parse the stack contents lines backwards, so we get to pile up the
+-- items from the bottom upwards. We can iterate over each found "["
+-- character, and from their position in the line determine in which
+-- stack they are: positions for the opening bracket are always multiples
+-- of four.
+for i = #stacks_lines, 1, -1 do
+   for bracketpos, label in stacks_lines[i]:gmatch("()%[(%a+)%]") do
+      local stacknum = (bracketpos // 4) + 1
+      table.insert(stacks[stacknum], label)
+   end
+end
+
+for line in io.lines() do
+   local _, _, n, from, to = line:find("move (%d+) from (%d+) to (%d+)")
+   for _ = 1, n do
+      from, to = tonumber(from), tonumber(to)
+      table.insert(stacks[to], table.remove(stacks[from]))
+   end
+end
+
+local result = {}
+for i = 1, nstacks do
+   local thisstack = stacks[i]
+   if #thisstack > 0 then
+      result[#result+1] = thisstack[#thisstack]
+   end
+end
+
+print(table.concat(result, ""))

@@ 0,0 1,9 @@
+    [D]    
+[N] [C]    
+[Z] [M] [P]
+ 1   2   3 
+
+move 1 from 2 to 1
+move 3 from 1 to 3
+move 2 from 2 to 1
+move 1 from 1 to 2