Thread: Complexity problem

I'm trying solve a problem which I have been able to code on a smaller scale though as soon as I start imputing larger values the time it takes increases considerably to the point where the final solution may take me a lifetime to find out.

The problem is Project Euler | Problem 12, I don't want the solution rather just guidance on a considerably more efficient collection type which may aid me.

The following is my own code:

public class abc{
  public static void main(String[] args){
	 for(int j=1;j<1000;j++){
	  List<Integer>ar = new ArrayList<Integer>();
	 for(int i=1;i<triangle(j)+1;i++){
      if(triangle(j)%i==0){
    	  ar.add(i);
      }
   	 }
 
	 if(ar.size()>5){
	 System.out.println(triangle(j));
	 break;
	 }	
	 }
	 }
 
 
  public static int triangle(int num){
	  if(num==1){
		  return 1;
	  }
	  return num +triangle(num-1);
  }
  }

I need to replace the 5 with a 500 to find the solution.

Do only what is necessary to answer the question. Simplify your program to something like:

1. Find the next triangle number
2. Find the number of factors in the triangle number
3 Report the first triangle number to have over 500 factors and stop, OR
4. Goto 1

My solution is simpler than yours and could be simplified some, but finding the answer takes a looooong time.