text: Store frequency of each element
code: for ( int i = 0 ; i < n ; i ++ ) { if ( mp . ContainsKey ( a [ i ] ) ) { var val = mp [ a [ i ] ] ; mp . Remove ( a [ i ] ) ; mp . Add ( a [ i ] , val + 1 ) ; } else { mp . Add ( a [ i ] , 1 ) ; } }