this is O ( N ^ 2 ) method
int p = - 1 , i , j ; for ( i = 0 ; i < s . length ( ) ; i ++ ) { for ( j = i + 1 ; j < s . length ( ) ; j ++ ) { if ( s . charAt ( i ) == s . charAt ( j ) ) { p = i ; break ; } } if ( p != - 1 ) break ; } return p ; }