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#!/opt/local/bin/lua
--
-- See ../README.md
--
--
-- Run as: lua ch-2.lua < input-file
--
--
-- Recursively count matches:
-- - If either the string or the pattern is empty, there are no matches.
-- - Else, + count the matches if we don't match at the first character
-- if the string.
-- + if the first character of the string equals the first
-- character of the pattern:
-- o add 1 if the pattern is just one character long
-- o else, add the number of matches starting from the
-- then next character in the string, and the next
-- character in the pattern.
--
function matches (str, pattern)
if str : len () == 0 or pattern : len () == 0 then
return 0
end
local count = matches (str : sub (2), pattern)
if str : sub (1, 1) == pattern : sub (1, 1) then
if pattern : len () == 1 then
count = count + 1
else
count = count + matches (str : sub (2), pattern : sub (2))
end
end
return (count)
end
--
-- Read input from standard input, assuming one exercise per line.
-- Each line consists of a string $S, and a pattern $T, separated
-- by whitespace.
--
for line in io . lines () do
local str, pattern = line : match ("(%S+) +(%S+)")
print (matches (str, pattern))
end
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