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const maxDistance = 3;
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function editDistance(a, b) {
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// https://en.wikipedia.org/wiki/Damerau–Levenshtein_distance
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// Calculating optimal string alignment distance, no substring is edited more than once.
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// (Simple implementation.)
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// Quick early exit, return worst case.
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if (Math.abs(a.length - b.length) > maxDistance) return Math.max(a.length, b.length);
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// distance between prefix substrings of a and b
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const d = [];
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// pure deletions turn a into empty string
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for (let i = 0; i <= a.length; i++) {
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d[i] = [i];
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}
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// pure insertions turn empty string into b
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for (let j = 0; j <= b.length; j++) {
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d[0][j] = j;
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}
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// fill matrix
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for (let j = 1; j <= b.length; j++) {
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for (let i = 1; i <= a.length; i++) {
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let cost = 1;
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if (a[i - 1] === b[j - 1]) {
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cost = 0;
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} else {
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cost = 1;
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}
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d[i][j] = Math.min(
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d[i - 1][j] + 1, // deletion
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d[i][j - 1] + 1, // insertion
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d[i - 1][j - 1] + cost // substitution
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);
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// transposition
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if (i > 1 && j > 1 && a[i - 1] === b[j - 2] && a[i - 2] === b[j - 1]) {
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d[i][j] = Math.min(d[i][j], d[i - 2][j - 2] + 1);
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}
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}
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}
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return d[a.length][b.length];
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}
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/**
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* Find close matches, restricted to same number of edits.
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*
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* @param {string} word
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* @param {string[]} candidates
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* @returns {string}
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*/
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function suggestSimilar(word, candidates) {
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if (!candidates || candidates.length === 0) return '';
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// remove possible duplicates
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candidates = Array.from(new Set(candidates));
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const searchingOptions = word.startsWith('--');
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if (searchingOptions) {
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word = word.slice(2);
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candidates = candidates.map(candidate => candidate.slice(2));
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}
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let similar = [];
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let bestDistance = maxDistance;
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const minSimilarity = 0.4;
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candidates.forEach((candidate) => {
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if (candidate.length <= 1) return; // no one character guesses
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const distance = editDistance(word, candidate);
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const length = Math.max(word.length, candidate.length);
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const similarity = (length - distance) / length;
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if (similarity > minSimilarity) {
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if (distance < bestDistance) {
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// better edit distance, throw away previous worse matches
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bestDistance = distance;
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similar = [candidate];
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} else if (distance === bestDistance) {
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similar.push(candidate);
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}
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}
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});
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similar.sort((a, b) => a.localeCompare(b));
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if (searchingOptions) {
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similar = similar.map(candidate => `--${candidate}`);
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}
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if (similar.length > 1) {
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return `\n(Did you mean one of ${similar.join(', ')}?)`;
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}
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if (similar.length === 1) {
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return `\n(Did you mean ${similar[0]}?)`;
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}
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return '';
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}
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exports.suggestSimilar = suggestSimilar;
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