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Difference between the largest and the smallest primes in an array in Java
Problem Statement
With a given array of integers where all elements are less than 1000000. Find the difference between the largest and the smallest primes in an array.
Example
Array: [ 1, 2, 3, 4, 5 ] Largest Prime Number = 5 Smallest Prime Number = 2 Difference = 5 - 3 = 2.
Solution
Use Sieve of Eratosthenes approach, which is an efficient way to find out all prime numbers smaller than a given number. Then we will figure out the largest and smallest prime number to get the required difference.
Example
Following is the program in Java to find the required output.
public class JavaTester {
static int MAX = 1000000;
static boolean prime[] = new boolean[MAX + 1];
public static void runSieveOfEratosthenes(){
//reset prime flags to be true
for(int i=0; i< MAX+1; i++) prime[i] = true;
//set 1 as non-prime
prime[1] = false;
for (int p = 2; p * p <= MAX; p++) {
// If prime[p] is not modified, then it is a prime
if (prime[p]) {
// Update all multiples of p
for (int i = p * 2; i <= MAX; i += p) prime[i] = false;
}
}
}
public static int difference(int arr[]){
int min = MAX + 2;
int max = -1;
for (int i = 0; i < arr.length; i++) {
// check if the number is prime or not
if (prime[arr[i]] == true) {
// set the max and min values
if (arr[i] > max) max = arr[i];
if (arr[i] < min) min = arr[i];
}
}
return max - min;
}
public static void main(String args[]){
// run the sieve
runSieveOfEratosthenes();
int arr[] = { 1, 2, 3, 4, 5 };
System.out.println(difference(arr));
}
}Output
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Updated on: 16-May-2020
750 Views
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