A Utility Function to find the common prefix between strings - str1 and str2
function commonPrefixUtil ( str1 , str2 ) { let result = " " ; let n1 = str1 . length , n2 = str2 . length ; for ( let i = 0 , j = 0 ; i <= n1 - 1 && j <= n2 - 1 ; i ++ , j ++ ) { if ( str1 [ i ] != str2 [ j ] ) { break ; } result += str1 [ i ] ; } return ( result ) ; }