49 lines
1.4 KiB
JavaScript
49 lines
1.4 KiB
JavaScript
(function (lstTest) {
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var mapping = [["M", 1000], ["CM", 900], ["D", 500], ["CD", 400], ["C", 100], [
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"XC", 90], ["L", 50], ["XL", 40], ["X", 10], ["IX", 9], ["V", 5], ["IV",
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4], ["I", 1]];
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// s -> n
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function romanValue(s) {
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// recursion over list of characters
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// [c] -> n
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function toArabic(lst) {
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return lst.length ? function (xs) {
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var lstParse = chain(mapping, function (lstPair) {
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return isPrefixOf(
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lstPair[0], xs
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) ? [lstPair[1], drop(lstPair[0].length, xs)] : []
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});
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return lstParse[0] + toArabic(lstParse[1]);
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}(lst) : 0
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}
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return toArabic(s.split(''));
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}
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// Monadic bind (chain) for lists
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function chain(xs, f) {
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return [].concat.apply([], xs.map(f));
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}
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// [a] -> [a] -> Bool
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function isPrefixOf(lstFirst, lstSecond) {
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return lstFirst.length ? (
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lstSecond.length ?
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lstFirst[0] === lstSecond[0] && isPrefixOf(
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lstFirst.slice(1), lstSecond.slice(1)
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) : false
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) : true;
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}
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// Int -> [a] -> [a]
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function drop(n, lst) {
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return n <= 0 ? lst : (
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lst.length ? drop(n - 1, lst.slice(1)) : []
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);
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}
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return lstTest.map(romanValue);
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})(['MCMXC', 'MDCLXVI', 'MMVIII']);
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