64 lines
1.3 KiB
Lua
64 lines
1.3 KiB
Lua
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-- see if the file exists
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local function file_exists(file)
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local f = io.open(file, "rb")
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if f then
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f:close()
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end
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return f ~= nil
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end
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-- get all lines from a file, returns an empty
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-- list/table if the file does not exist
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local function lines_from(file)
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if not file_exists(file) then
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return {}
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end
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local lines = {}
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for line in io.lines(file) do
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lines[#lines + 1] = line
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end
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return lines
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end
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-- tests the functions above
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local file = "input"
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local lines = lines_from(file)
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local left_list = {}
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local right_list = {}
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-- https://www.lua.org/manual/5.4/manual.html#pdf-ipairs
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-- print all line numbers and their contents
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for _, v in ipairs(lines) do
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for n1, n2 in string.gmatch(v, "(%d+)%s+(%d+)") do
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-- [](https://stackoverflow.com/a/27434198)
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-- [Lua Length Operator](https://www.lua.org/manual/5.2/manual.html#3.4.6)
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left_list[#left_list + 1] = n1
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right_list[#right_list + 1] = n2
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end
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end
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local right_list_count_map = {}
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for _, v in ipairs(right_list) do
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if right_list_count_map[v] ~= nil then
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right_list_count_map[v] = right_list_count_map[v] + 1
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else
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right_list_count_map[v] = 1
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end
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end
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local total = 0
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for _, v in ipairs(left_list) do
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local count
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if right_list_count_map[v] ~= nil then
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count = right_list_count_map[v]
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else
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count = 0
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end
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total = total + (v * count)
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end
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io.output():write(total)
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