if the characters contained in the two sets are same , return true
if ( ( diff [ 0 ] [ 0 ] == diff [ 1 ] [ 0 ] and diff [ 0 ] [ 1 ] == diff [ 1 ] [ 1 ] ) or ( diff [ 0 ] [ 0 ] == diff [ 1 ] [ 1 ] and diff [ 0 ] [ 1 ] == diff [ 1 ] [ 0 ] ) ) return true ; } return false ; }