11/**
2- *@param {string }s1
3- *@param {string }s2
2+ *@param {string }string1
3+ *@param {string }string2
44 *@return {string }
55 */
6- export default function longestCommonSubstring ( s1 , s2 ) {
7- // transform s1 & s2 into arrays to allow handling unicodes as single caracter.
8- const [ a1 , a2 ] = [ s1 , s2 ] . map ( s => Array . from ( s ) ) ;
6+ export default function longestCommonSubstring ( string1 , string2 ) {
7+ // Convert strings to arrays to treat unicode symbols length correctly.
8+ // For example:
9+ // '𐌵'.length === 2
10+ // [...'𐌵'].length === 1
11+ const s1 = [ ...string1 ] ;
12+ const s2 = [ ...string2 ] ;
913
1014// Init the matrix of all substring lengths to use Dynamic Programming approach.
11- const substringMatrix = Array ( a2 . length + 1 ) . fill ( null ) . map ( ( ) => {
12- return Array ( a1 . length + 1 ) . fill ( null ) ;
15+ const substringMatrix = Array ( s2 . length + 1 ) . fill ( null ) . map ( ( ) => {
16+ return Array ( s1 . length + 1 ) . fill ( null ) ;
1317} ) ;
1418
1519// Fill the first row and first column with zeros to provide initial values.
16- for ( let columnIndex = 0 ; columnIndex <= a1 . length ; columnIndex += 1 ) {
20+ for ( let columnIndex = 0 ; columnIndex <= s1 . length ; columnIndex += 1 ) {
1721substringMatrix [ 0 ] [ columnIndex ] = 0 ;
1822}
1923
20- for ( let rowIndex = 0 ; rowIndex <= a2 . length ; rowIndex += 1 ) {
24+ for ( let rowIndex = 0 ; rowIndex <= s2 . length ; rowIndex += 1 ) {
2125substringMatrix [ rowIndex ] [ 0 ] = 0 ;
2226}
2327
@@ -26,9 +30,9 @@ export default function longestCommonSubstring(s1, s2) {
2630let longestSubstringColumn = 0 ;
2731let longestSubstringRow = 0 ;
2832
29- for ( let rowIndex = 1 ; rowIndex <= a2 . length ; rowIndex += 1 ) {
30- for ( let columnIndex = 1 ; columnIndex <= a1 . length ; columnIndex += 1 ) {
31- if ( a1 [ columnIndex - 1 ] === a2 [ rowIndex - 1 ] ) {
33+ for ( let rowIndex = 1 ; rowIndex <= s2 . length ; rowIndex += 1 ) {
34+ for ( let columnIndex = 1 ; columnIndex <= s1 . length ; columnIndex += 1 ) {
35+ if ( s1 [ columnIndex - 1 ] === s2 [ rowIndex - 1 ] ) {
3236substringMatrix [ rowIndex ] [ columnIndex ] = substringMatrix [ rowIndex - 1 ] [ columnIndex - 1 ] + 1 ;
3337} else {
3438substringMatrix [ rowIndex ] [ columnIndex ] = 0 ;
@@ -53,7 +57,7 @@ export default function longestCommonSubstring(s1, s2) {
5357let longestSubstring = '' ;
5458
5559while ( substringMatrix [ longestSubstringRow ] [ longestSubstringColumn ] > 0 ) {
56- longestSubstring = a1 [ longestSubstringColumn - 1 ] + longestSubstring ;
60+ longestSubstring = s1 [ longestSubstringColumn - 1 ] + longestSubstring ;
5761longestSubstringRow -= 1 ;
5862longestSubstringColumn -= 1 ;
5963}