Multiples of 3 or 5

Question

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6, 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Solution

This problem is essentially checking the exact same logic as Fizzbuzz, so I feel there isn’t much to be said about the fundamentals of the math and logic behind this.

The Go language, however, has a semantically convenient and syntactically beautiful way to implement this. Instead of writing cascading if {} else if {} else {} statements that get tedious and ugly, switch statements without arguments are used. A switch statement without an argument is the same as writing switch true, meaning it will evaluate each case in order until one evaluates to true. This allows me to write more readable code, while also bypassing any extraneous redundancy checking.

// Returns the sum of all multiples of 3 and 5 below n.
func sumThreeFive(n uint64) sum uint64 {
    sum = 0
	for i := uint64(0); i < n; i++ {
		switch {
		case i%3 == 0:
			sum += i
		case i%5 == 0:
			sum += i
		}
	}
	return sum
}

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