Java Program for Find largest prime factor of a number

Last Updated : 17 Feb, 2018

Given a positive integer \’n\'( 1 <= n <= 10¹⁵). Find the largest prime factor of a number.

Input: 6
Output: 3
Explanation
Prime factor of 6 are- 2, 3
Largest of them is \'3\'

Input: 15
Output: 5

Java

// Java Program to find largest 
// prime factor of number 
import java.io.*; 
import java.util.*; 
  
class GFG { 
  
// function to find largest prime factor 
static long maxPrimeFactors( long n) 
{ 
    // Initialize the maximum prime 
    // factor variable with the  
    // lowest one 
    long maxPrime = -1; 
  
    // Print the number of 2s 
    // that divide n 
    while (n % 2 == 0) { 
        maxPrime = 2; 
          
        // equivalent to n /= 2 
        n >>= 1;  
    } 
  
    // n must be odd at this point, 
    // thus skip the even numbers  
    // and iterate only for odd 
    // integers 
    for (int i = 3; i <= Math.sqrt(n); i += 2) { 
        while (n % i == 0) { 
            maxPrime = i; 
            n = n / i; 
        } 
    } 
  
    // This condition is to handle  
    // the case when n is a prime  
    // number greater than 2 
    if (n > 2) 
        maxPrime = n; 
  
    return maxPrime; 
} 
  
// Driver code 
public static void main(String[] args) 
{ 
    Long n = 15l; 
    System.out.println(maxPrimeFactors(n)); 
  
    n = 25698751364526l; 
    System.out.println(maxPrimeFactors(n)); 
} 
} 
  
// This code is contributed by Gitanjali 

Output:

5
328513

Time complexity: $\text{O}(\sqrt{n})$ Auxiliary space: $\text{O}(1)$ Please refer complete article on Find largest prime factor of a number for more details!

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