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p012.java
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45 lines (37 loc) · 1.09 KB
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/*
* Solution to Project Euler problem 12
* Copyright (c) Project Nayuki. All rights reserved.
*
* https://www.nayuki.io/page/project-euler-solutions
* https://github.com/nayuki/Project-Euler-solutions
*/
public final class p012 implements EulerSolution {
public static void main(String[] args) {
System.out.println(new p012().run());
}
/*
* Computers are fast, so we can implement this solution directly without any clever math.
*/
public String run() {
int triangle = 0;
for (int i = 1; ; i++) {
if (Integer.MAX_VALUE - triangle < i)
throw new ArithmeticException("Overflow");
triangle += i; // This is the ith triangle number, i.e. num = 1 + 2 + ... + i = i * (i + 1) / 2
if (countDivisors(triangle) > 500)
return Integer.toString(triangle);
}
}
// Returns the number of integers in the range [1, n] that divide n.
private static int countDivisors(int n) {
int count = 0;
int end = Library.sqrt(n);
for (int i = 1; i < end; i++) {
if (n % i == 0)
count += 2;
}
if (end * end == n) // Perfect square
count++;
return count;
}
}