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Java Program to find largest prime factor of a number
Following is the Java code to find the largest prime factor of a number −
Example
import java.io.*;
import java.util.*;
public class Demo{
static long maxPrimeFactors( long val){
long max_prime = -1;
while (val % 2 == 0) {
max_prime = 2;
val >>= 1;
}
for (int i = 3; i <= Math.sqrt(val); i += 2){
while (val % i == 0){
max_prime = i;
val = val / i;
}
}
if (val > 2)
max_prime = val;
return max_prime;
}
public static void main(String[] args){
int val = 148592;
System.out.println("The largest prime factor of 148592 is ");
System.out.println(maxPrimeFactors(val));
val = 890654;
System.out.println("The largest prime factor of 890654 is ");
System.out.println(maxPrimeFactors(val));
}
}Output
The largest prime factor of 148592 is 251 The largest prime factor of 890654 is 4591
A class named Demo contains a static function that tales a value, and a ‘while’ condition is defined, which checks whether the value modulus 2 is 0. If it is 0, then, a variable (max_prime) is assigned the value 2. Otherwise, it is right bit shifted by 1. Again, a ‘for’ loop is iterated over elements from 3 to square root of the value, and incremented by 2 after every iteration.
Now, a ‘while’ loop checks if the value modulus iterator is 0. If yes, a variable (max_prime) is assigned the value that is currently being iterated. The value is divided by the iterated value. If this value is greater than 2, then this value (max_prime) is assigned to a variable named max_prime. This is returned. In the main function, an integer value is defined and the largest prime factor is found out by calling the function with the specific argument.
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