Sort prime numbers of an array in descending order | Java implementation of the approach ; false here indicates that it is not prime ; If prime [ p ] is not changed , then it is a prime ; Update all multiples of p , set them to non - prime ; Function that sorts all the prime numbers from the array in descending ; this vector will contain prime numbers to sort ; if the element is prime ; update the array elements ; Driver code ; print the results .
import java . util . * ; class GFG { static boolean prime [ ] = new boolean [ 100005 ] ; static void SieveOfEratosthenes ( int n ) { Arrays . fill ( prime , true ) ; prime [ 1 ] = false ; for ( int p = 2 ; p * p <= n ; p ++ ) { if ( prime [ p ] ) { for ( int i = p * 2 ; i < n ; i += p ) { prime [ i ] = false ; } } } } static void sortPrimes ( int arr [ ] , int n ) { SieveOfEratosthenes ( 100005 ) ; Vector < Integer > v = new Vector < Integer > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { if ( prime [ arr [ i ] ] ) { v . add ( arr [ i ] ) ; } } Comparator comparator = Collections . reverseOrder ( ) ; Collections . sort ( v , comparator ) ; int j = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( prime [ arr [ i ] ] ) { arr [ i ] = v . get ( j ++ ) ; } } } public static void main ( String [ ] args ) { int arr [ ] = { 4 , 3 , 2 , 6 , 100 , 17 } ; int n = arr . length ; sortPrimes ( arr , n ) ; for ( int i = 0 ; i < n ; i ++ ) { System . out . print ( arr [ i ] + " ▁ " ) ; } } }