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ch-2.js
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ch-2.js
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#!/usr/local/bin/node
//
// See ../README.md
//
//
// Run as: node ch-2.js < input-file
//
//
// Read input from standard input, assuming one exercise per line.
// Each line consists of a string $S, and a pattern $T, separated
// by whitespace.
//
require ('readline')
. createInterface ({input: process . stdin})
. on ('line', _ => console . log (matches (... _ . split (' '))))
;
//
// 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 (string, pattern) {
if (string . length == 0 || pattern . length == 0) {
return 0
}
let count = matches (string . substring (1), pattern);
if (string . substring (0, 1) == pattern . substring (0, 1)) {
if (pattern . length == 1) {
count ++
}
else {
count += matches (string . substring (1), pattern . substring (1))
}
}
return count
}