Explicitly handle corner cases [ 10 , 19 ]
if ( num [ x ] . charCodeAt ( 0 ) - ' ' . charCodeAt ( 0 ) == 1 ) { let sum = num [ x ] . charCodeAt ( 0 ) - ' ' . charCodeAt ( 0 ) + num [ x ] . charCodeAt ( 0 ) - ' ' . charCodeAt ( 0 ) ; ans += two_digits [ sum ] ; return ans ; }