Java Program: Lambda expression to find largest prime factor

Last update on May 07 2025 13:04:33 (UTC/GMT +8 hours)

24. Find largest prime factor using lambda

Write a Java program to implement a lambda expression to find the largest prime factor of a given number.

Sample Solution:

Java Code:

import java.util.stream.LongStream;

public class Main {
  public static void main(String[] args) {
    int n = 176;
    System.out.println("Number: " + n);

    long largestPrimeFactor = findLargestPrimeFactor(n);
    System.out.println("Largest prime factor: " + largestPrimeFactor);
    n = 36;
    System.out.println("\nNumber: " + n);

    largestPrimeFactor = findLargestPrimeFactor(n);
    System.out.println("Largest prime factor: " + largestPrimeFactor);
  }

  public static long findLargestPrimeFactor(long n) {
    for (long i = (long) Math.sqrt(n); i >= 2; i--) {
      if (n % i == 0 && isPrime(i)) {
        return i;
      }
    }
    return n;
  }

  public static boolean isPrime(long number) {
    return LongStream.rangeClosed(2, (long) Math.sqrt(number))
      .allMatch(n -> number % n != 0);
  }
}

Sample Output:

Number: 176
Largest prime factor: 11

Number: 36
Largest prime factor: 3

Explanation:

Main() method:

Initializes a variable n with a value.
Calls the findLargestPrimeFactor() method to calculate the largest prime factor of n.
Prints the largest prime factor.

findLargestPrimeFactor(long n) method :

It takes a long integer n as input.
It iterates from the square root of n (converted to a long) downwards to 2.
Inside the loop, it checks if n is divisible by the current value of i and if i is a prime number by calling the isPrime method.
If both conditions are satisfied, it returns i, which is the largest prime factor.
If no prime factors are found, it returns the original number n.

isPrime(long number):

It takes a long integer number as input.
It uses a LongStream to generate a range of numbers from 2 to the square root of number, inclusive.
It checks if all numbers in the range satisfy the condition that number is not divisible evenly by any of them.
If all numbers in the range satisfy the condition, it returns true, indicating that number is a prime number.
If any number in the range divides number evenly, it returns false.

Flowchart:

For more Practice: Solve these Related Problems:

Write a Java program to implement a lambda expression that finds the largest prime factor of a number using stream reduction.
Write a Java program to create a lambda that factors a number into primes and then extracts the maximum using a custom comparator.
Write a Java program to implement a lambda expression that checks each divisor of a number for primality and selects the largest.
Write a Java program to chain lambda expressions to generate factors of a number, filter for primes, and then find the maximum factor.

Go to:

Improve this sample solution and post your code through Disqus

PREV : Find average string length using lambda.
NEXT : Convert integer to binary using lambda.

Live Demo:

Java Code Editor: