Put all elements in a hash map
Map < Integer , Integer > mp = new HashMap < > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { if ( mp . containsKey ( arr [ i ] ) ) { mp . put ( arr [ i ] , mp . get ( arr [ i ] ) + 1 ) ; } else { mp . put ( arr [ i ] , 1 ) ; } }