project-euler/projectEuler028.cpp at master · perfectsimulation/project-euler · GitHub

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/*	Problem 28
	Number Spiral Diagonals

	Starting with the number 1 and moving to the right in a clockwise
	direction a 5 by 5 spiral is formed as follows:

	21 22 23 24 25
	20  7  8  9 10
	19  6  1  2 11
	18  5  4  3 12
	17 16 15 14 13

	It can be verified that the sum of the numbers on the diagonals is 101.

	What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral
	formed in the same way?
*/

#include <iomanip>
#include <iostream>

using namespace std;

int main () {
	double sumDiagonals = 1;
	int lastTerm = 1;

	for (int i = 1; i <= 500; i++) {
		for (int j = 1; j <= 4; j++) {
			sumDiagonals += double (2*(i * j) + lastTerm);
			if (j == 4) {
				lastTerm = 2*(i * j) + lastTerm;
			}
		}
	}

	cout << setprecision (0) << fixed;
	cout << sumDiagonals << endl;

}