TheAlgorithms-C/project_euler/Problem 01/sol3.c

/*
If we list all the natural numbers below 10 that are multiples of 3 or 5,
we get 3,5,6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below N.
'''
'''
This solution is based on the pattern that the successive numbers in the series follow: 0+3,+2,+1,+3,+1,+2,+3.
*/
#include <stdio.h>

int main() {
	int n = 0;
	int sum = 0;
	int num = 0;
	scanf("%d", &n);
	
	while (1) {
		num += 3;
		if (num >= n)
			break;
		sum += num;
		num += 2;
		if (num >= n)
			break;
		sum += num;
		num += 1;
		if (num >= n) 
			break;
		sum += num;
		num += 3;
		if (num >= n) 
			break;
		sum += num;
		num += 1;
		if (num >= n) 
			break;
		sum += num;
		num += 2;
		if (num >= n) 
			break;
		sum += num;
		num += 3;
		if (num >= n) 
				break;
		sum += num;
	}

	printf("%d\n", sum);
}