Euler 28

gistfile1.txt

#!/usr/local/bin/node

/*	this is the pattern formed by the diagonals
ring 2  -- 2+ ([+1] +  3 + [+2] +  5 + [+2] +  7 + [+2])+ 9    
ring 3  -- 10+([+3] + 13 + [+4] + 17 + [+4] + 21 + [+4])+25 
where the numbers in brackets increase by 2 each time

how many rings?  well ring 1 is a 1x1
and then every ring after adds 2 columns or rows
so by ring 2 you have 3 rows and 3 columns
by ring 3 you have 5 rows and 5 columns
by ring 4 you have 7 rows and 7 columns
so each ring adds 2
so you need 500 rings to get to get 1001 rows by 1001 columns
*/


total = 1;
term = 2; 
diagonal_total = 1;
for(i=1;i<=500;i++)
	{
	start = total + 1;
	a = start + (term-1);
	b = a + term;
	c = b + term;
	d = c + term;
//	console.log("ring " + i + " is " + a+" "+b+" "+c+" "+d+ " equals "+ (a+b+c+d));
	diagonal_total += (a+b+c+d);
	total = d;
	term +=2;
	}
console.log(diagonal_total);