Initial Commit

go/sum-of-multiples/README.md

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+# Sum Of Multiples
+
+Write a program that, given a number, can find the sum of all the multiples of particular numbers up to but not including that number.
+
+If we list all the natural numbers up to but not including 15 that are
+multiples of either 3 or 5, we get 3, 5, 6 and 9, 10, and 12.
+
+The sum of these multiples is 45.
+
+Write a program that can find the sum of the multiples of a given set of
+numbers.
+
+To run the tests simply run the command `go test` in the exercise directory.
+
+If the test suite contains benchmarks, you can run these with the `-bench`
+flag:
+
+    go test -bench .
+
+For more detailed info about the Go track see the [help
+page](http://help.exercism.io/getting-started-with-go.html).
+
+## Source
+
+A variation on Problem 1 at Project Euler [view source](http://projecteuler.net/problem=1)

go/sum-of-multiples/sum_of_multiples_test.go

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+package summultiples
+
+import "testing"
+
+var test35 = []struct {
+	limit int
+	sum   int
+}{
+	{1, 0},
+	{4, 3},
+	{10, 23},
+	{1000, 233168},
+}
+
+var varTests = []struct {
+	divisors []int
+	limit    int
+	sum      int
+}{
+	{[]int{7, 13, 17}, 20, 51},
+	{[]int{43, 47}, 10000, 2203160},
+	{[]int{5, 10, 12}, 10000, 13331672},
+	{[]int{1, 1}, 10000, 49995000},
+	{[]int{}, 10000, 0},
+}
+
+func Test35(t *testing.T) {
+	sum35 := MultipleSummer(3, 5)
+	for _, test := range test35 {
+		s := sum35(test.limit)
+		if s != test.sum {
+			t.Fatalf("Sum to %d returned %d, want %d.", test.limit, s, test.sum)
+		}
+	}
+}
+
+func TestVar(t *testing.T) {
+	for _, test := range varTests {
+		sv := MultipleSummer(test.divisors...)
+		s := sv(test.limit)
+		if s != test.sum {
+			t.Fatalf("Sum of multiples of %v to %d returned %d, want %d.",
+				test.divisors, test.limit, s, test.sum)
+		}
+	}
+}
+
+func Benchmark35(b *testing.B) {
+	sum35 := MultipleSummer(3, 5)
+	b.ResetTimer() // bench just the sum function
+	for i := 0; i < b.N; i++ {
+		for _, test := range test35 {
+			sum35(test.limit)
+		}
+	}
+}
+
+func BenchmarkVar(b *testing.B) {
+	// bench combined time to bind sum function and call it.
+	for i := 0; i < b.N; i++ {
+		for _, test := range varTests {
+			MultipleSummer(test.divisors...)(test.limit)
+		}
+	}
+}

go/sum-of-multiples/summultiples.go

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+package summultiples
+
+// MultipleSummer takes a variable number of ints
+// and returns a function that, when given a limit
+// returns the sum of the multiples up to that limit
+func MultipleSummer(mults ...int) func(int) int {
+	return func(limit int) int {
+		var ret int
+		for i := range mults {
+			sumMult := mults[i]
+			for sumMult < limit {
+				var skip bool
+				for j := 0; j < i && !skip; j++ {
+					// Make sure that we haven't already added sumMult
+					if sumMult%mults[j] == 0 {
+						skip = true
+					}
+				}
+				if !skip {
+					ret += sumMult
+				}
+				sumMult += mults[i]
+			}
+		}
+		return ret
+	}
+}