Store occurrences of all elements in hash array
Map < Integer , Integer > m = new HashMap < > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { if ( m . containsKey ( arr [ i ] ) ) { m . put ( arr [ i ] , m . get ( arr [ i ] ) + 1 ) ; } else { m . put ( arr [ i ] , m . get ( arr [ i ] ) ) ; } }