Java Program: Lambda expression to find largest prime factor

Last update on April 28 2025 07:58:29 (UTC/GMT +8 hours)

Find Largest Prime Factor of a Given Number

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.

Live Demo:

Java Code Editor:

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