Fix levenshteinDistance for Unicode characters

Author: dubzzz

src/algorithms/string/levenshtein-distance/__test__/levenshteinDistance.test.js

@@ -51,10 +51,7 @@ describe('levenshteinDistance', () => {
       fc.fullUnicodeString(),
       (aBegin, aEnd, bBegin, bEnd, common) =>
         levenshteinDistance(aBegin + common + aEnd, bBegin + common + bEnd)
-          <= Math.max(aBegin.length, bBegin.length) + Math.max(aEnd.length, bEnd.length)
-        // @TODO: Provide Unicode support for characters outside of the BMP plan.
-        // @TODO: Replace previous line by the one below:
-        //  <= Math.max([...aBegin].length, [...bBegin].length) + Math.max([...aEnd].length, [...bEnd].length)
+          <= Math.max([...aBegin].length, [...bBegin].length) + Math.max([...aEnd].length, [...bEnd].length)
     )
   ));
 });

src/algorithms/string/levenshtein-distance/levenshteinDistance.js

@@ -3,7 +3,13 @@
  * @param {string} b
  * @return {number}
  */
-export default function levenshteinDistance(a, b) {
+export default function levenshteinDistance(aRaw, bRaw) {
+  // Split strings a and b in characters
+  // In JavaScript '\u{1f431}' has a length of 2 while it is a single character
+  // Array.from(string) or [...string] can extract those characters properly
+  const a = Array.from(aRaw);
+  const b = Array.from(bRaw);
+
   // Create empty edit distance matrix for all possible modifications of
   // substrings of a to substrings of b.
   const distanceMatrix = Array(b.length + 1).fill(null).map(() => Array(a.length + 1).fill(null));