Returns LCS X and Y
function lcs ( a , b ) { let m = a . length ; let n = b . length ; let X = a . split ( ' ' ) ; let Y = b . split ( ' ' ) ; let L = new Array ( m + 1 ) ; for ( let i = 0 ; i <= m ; i ++ ) { L [ i ] = new Array ( n + 1 ) ; for ( let j = 0 ; j <= n ; j ++ ) { L [ i ] [ j ] = 0 ; } }