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Problem03.java

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Problem03.java

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package ProjectEuler;
/**
* The prime factors of 13195 are 5, 7, 13 and 29.
*
* <p>What is the largest prime factor of the number 600851475143 ?
*
* <p>Link: https://projecteuler.net/problem=3
*/
public class Problem03 {
/**
* Checks if a number is prime or not
*
* @param n the number
* @return {@code true} if {@code n} is prime
*/
public static boolean isPrime(int n) {
if (n == 2) {
return true;
}
if (n < 2 || n % 2 == 0) {
return false;
}
for (int i = 3, limit = (int) Math.sqrt(n); i <= limit; i += 2) {
if (n % i == 0) {
return false;
}
}
return true;
}
/**
* Calculate all the prime factors of a number and return the largest
*
* @param n integer number
* @return the maximum prime factor of the given number
*/
static long maxPrimeFactor(long n) {
for (int i = 2; i < n / 2; i++) {
if (isPrime(i))
while (n % i == 0) {
n /= i;
}
}
return n;
}
public static void main(String[] args) {
int[][] testNumbers = {
{87, 29},
{10, 5},
{21, 7},
{657, 73},
{777, 37}
};
for (int[] num : testNumbers) {
assert Problem03.maxPrimeFactor(num[0]) == num[1];
}
assert Problem03.maxPrimeFactor(600851475143L) == 6857;
}
}
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