91 lines
2 KiB
Lua
91 lines
2 KiB
Lua
-- 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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-- Solution Starts here
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---@diagnostic disable-next-line: redefined-local
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local function count_xmas_at_index(lines, line_idx, char_idx)
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local line = lines[line_idx]
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local up_idx = line_idx - 1
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local down_idx = line_idx + 1
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local right_idx = char_idx + 1
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local left_idx = char_idx - 1
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local char_count = {}
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char_count["M"] = 0
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char_count["S"] = 0
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if up_idx >= 1 then
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if right_idx <= #line then
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local key = lines[up_idx]:sub(right_idx, right_idx)
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if char_count[key] ~= nil then
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char_count[key] = char_count[key] + 1
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end
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end
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if left_idx >= 1 then
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local key = lines[up_idx]:sub(left_idx, left_idx)
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if char_count[key] ~= nil then
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char_count[key] = char_count[key] + 1
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end
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end
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end
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if down_idx <= #lines then
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if right_idx <= #line then
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local key = lines[down_idx]:sub(right_idx, right_idx)
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if char_count[key] ~= nil then
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char_count[key] = char_count[key] + 1
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end
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end
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if left_idx >= 1 then
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local key = lines[down_idx]:sub(left_idx, left_idx)
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if char_count[key] ~= nil then
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char_count[key] = char_count[key] + 1
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end
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end
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end
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if char_count["M"] == 2 and char_count["S"] == 2 then
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return true
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end
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return false
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end
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local xmas_count = 0
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-- print all line numbers and their contents
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---@diagnostic disable-next-line: unused-local
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for line_idx, line in ipairs(lines) do
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for char_idx in line:gmatch("()A") do
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if count_xmas_at_index(lines, line_idx, char_idx) then
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xmas_count = xmas_count + 1
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end
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end
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end
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io.output():write(xmas_count)
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