text: Map is used to store element frequencies
code: Dictionary < int , int > m = new Dictionary < int , int > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { if ( m . ContainsKey ( arr [ i ] ) ) { var val = m [ arr [ i ] ] ; m . Remove ( arr [ i ] ) ; m . Add ( arr [ i ] , val + 1 ) ; } else { m . Add ( arr [ i ] , 1 ) ; } } int sum = 0 ;