ProjectEuler

Project Euler Sample Answers

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1 Multiples of 3 and 5

public class Main {
	public static void main(String[] args) {
		int sum = 0;
		for(int i = 0; i < 1000; i++) {
			if( (i%3 == 0) || (i%5 == 0) ) {
				sum+=i;
			}
		}
		System.out.println("Sum is " + sum);
	}
}

2 Even Fibonacci Numbers

public class Main {
	public static void main(String[] args) {
		int sum = 0, fib = 1, prev = 1, temp = 0;
		while(fib < 4000000) {
			temp = prev;
			prev = fib;
			fib = fib + temp;
			if(fib%2 == 0) {
				sum+=fib;
			}
		}
		System.out.println("Sum is " + sum);
	}
}

3 Largest Prime Factor

public class Main {
	public static void main(String[] args) {
		long prime = 1;
		long num = 600851475143L;
		long i = 2;
		while(i < num) {
			while(num%i == 0) {
				System.out.println("num: " + num + ", i: " + i);
				num =  num/i;
			}
			i++;
		}
		prime = num;
		System.out.println("Factor is " + prime);
	}
}

4 Largest palindrome product

import java.util.*;

public class Main {
	public static void main(String[] args) {
		ArrayList<Integer> Palindromes = new ArrayList<>();
		for(int i = 999; i > 100; i--) {
			for(int j = 999; j > 100; j--) {
				if(isPalindrome(i*j)) {
					Palindromes.add(i*j);
				}
			}
		}
		System.out.println("Largest palindrome is: " + Collections.max(Palindromes));
	}

	public static boolean isPalindrome(int n) {
		int temp = n, rem, rev = 0;
		while (temp != 0) {
	        rem = temp % 10;
	        rev = rev * 10 + rem;
	        temp = temp / 10;
	    }
		return n == rev;
	}
}