package euler

// SumMultiples finds the sum of all the multiples of 3 or 5 below 1000
func SumMultiples() int {
	result := 0

	for i := range [1000]int{} {
		if i%3 == 0 || i%5 == 0 {
			result += i
		}
	}

	return result
}

// EvenFibonacci finds the sum of the even-valued terms of a Fibonacci sequence,
// considering only the terms whose values do not exceed max
func EvenFibonacci(max int) int {
	result := 0
	first, second := 0, 1

	for second <= max {
		first, second = second, first+second

		if second%2 == 0 {
			result += second
		}
	}

	return result
}

// FindLargestPrimeFactor finds the largest prime factor of the number x
func FindLargestPrimeFactor(x int) int {

	isPrime := func(n int) bool {

		// Check if n=1 or n=0
		if n <= 1 {
			return false
		}

		// Check if n=2 or n=3
		if n == 2 || n == 3 {
			return true
		}

		// Check whether n is divisible by 2 or 3
		if n%2 == 0 || n%3 == 0 {
			return false
		}

		// Check from 5 to square root of n
		// Iterate i by (i+6)
		for i := 5; i*i <= n; i = i + 6 {
			if n%i == 0 || n%(i+2) == 0 {
				return false
			}
		}

		return true
	}

	if x == 2 || x == 3 {
		return x
	}

	for x%2 == 0 {
		x /= 2
	}

	for x%3 == 0 {
		x /= 3
	}

	largest := 0
	for i := 5; i <= x; i = i + 1 {
		if x%i == 0 {
			for x%i == 0 {
				x /= i
			}

			if isPrime(i) {
				largest = i
			}
		}
	}
	return largest
}