text: Hash array to set which character is present in the current string
code: var hash = Array ( MAX ) . fill ( 0 ) ; for ( var j = 0 ; j < str . length ; j ++ ) { hash [ str [ j ] . charCodeAt ( 0 ) - ' ' . charCodeAt ( 0 ) ] = true ; } for ( var j = 0 ; j < MAX ; j ++ ) {