Project Euler #12. What is the value of the first triangle number to have over five hundred divisors? I felt that this problem was easier than the last two, but I got stuck on line 29 and had to look up online for help. I want to come back to this problem and make it smoother. It is about 1.1 seconds, but it should be able to run at like 50ms wi…

TriangleNumber.java

public class TriangleNumber {
  
	private int numDivisors;
	
	public TriangleNumber(int numDivisors){ //takes in how many divisors
		this.numDivisors = numDivisors;
	}
	
	public int firstOccurance(){ //returns the first occurance of the number of divisors you want the triangle number to have
		int i = 1;
		int triNum = 0;
		while(true){
			if(divisorCounter(triNum) > this.numDivisors){ //when divisors for the triangle number
				break;
			}
			triNum += i; //goes to next triangle num
			++i;
		}
		return triNum;
	}

	public int divisorCounter(int number){  //figures number of divisors
		int counter = 0;
		for(int i = 1; i <= Math.sqrt(number); ++i){
			if(number % i == 0){
				counter += 2;
			}
		}
		if(Math.sqrt(number) * Math.sqrt(number) == number){ //kept going too high on the triangle number, found that this was the reason
			counter--;
		}
		return counter; //returns number of divisors
	}
	
	public static void main(String[] args){
		long begin = System.currentTimeMillis();
		TriangleNumber tri = new TriangleNumber(500);
		System.out.println(tri.firstOccurance());
		System.out.println(System.currentTimeMillis() - begin);
	}
}