sort the elements
sort ( a , a + n ) ; int num1 = 0 ; int num2 = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( i % 2 == 0 ) num1 = num1 * 10 + a [ i ] ; else num2 = num2 * 10 + a [ i ] ; } return num2 + num1 ; }