Find prime number K in an array such that ( A [ i ] % K ) is maximum | C ++ implementation of the approach ; Function to return the required prime number from the array ; Find maximum value in the array ; USE SIEVE TO FIND ALL PRIME NUMBERS LESS THAN OR EQUAL TO max_val Create a boolean array " prime [ 0 . . n ] " . A value in prime [ i ] will finally be false if i is Not a prime , else true . ; Remaining part of SIEVE ; If prime [ p ] is not changed , then it is a prime ; Update all multiples of p ; To store the maximum prime number ; If current element is prime then update the maximum prime ; Return the maximum prime number from the array ; Driver code
#include <bits/stdc++.h> NEW_LINE using namespace std ; int getPrime ( int arr [ ] , int n ) { int max_val = * max_element ( arr , arr + n ) ; vector < bool > prime ( max_val + 1 , true ) ; prime [ 0 ] = false ; prime [ 1 ] = false ; for ( int p = 2 ; p * p <= max_val ; p ++ ) { if ( prime [ p ] == true ) { for ( int i = p * 2 ; i <= max_val ; i += p ) prime [ i ] = false ; } } int maximum = -1 ; for ( int i = 0 ; i < n ; i ++ ) { if ( prime [ arr [ i ] ] ) maximum = max ( maximum , arr [ i ] ) ; } return maximum ; } int main ( ) { int arr [ ] = { 2 , 10 , 15 , 7 , 6 , 8 , 13 } ; int n = sizeof ( arr ) / sizeof ( arr [ 0 ] ) ; cout << getPrime ( arr , n ) ; return 0 ; }