Initial Commit

go/difference-of-squares/README.md

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+# Difference Of Squares
+
+Find the difference between the sum of the squares and the square of the sums of the first N natural numbers.
+
+The square of the sum of the first ten natural numbers is,
+
+    (1 + 2 + ... + 10)**2 = 55**2 = 3025
+
+The sum of the squares of the first ten natural numbers is,
+
+    1**2 + 2**2 + ... + 10**2 = 385
+
+Hence the difference between the square of the sum of the first
+ten natural numbers and the sum of the squares is 2640:
+
+    3025 - 385 = 2640
+
+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
+
+Problem 6 at Project Euler [view source](http://projecteuler.net/problem=6)

go/difference-of-squares/difference_of_squares.go

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+package diffsquares
+
+import "math"
+
+// SquareOfSums calculates the Square of the sums
+// of the first 'num' natural numbers
+func SquareOfSums(num int) int {
+	ret := 0
+	for num > 0 {
+		ret += num
+		num--
+	}
+	return int(math.Pow(float64(ret), 2))
+}
+
+// SumOfSquares calculates the Sum of the Squares
+// of the first 'num' natural numbers
+func SumOfSquares(num int) int {
+	ret := 0
+	for num > 0 {
+		ret += int(math.Pow(float64(num), 2))
+		num--
+	}
+	return ret
+}
+
+// Difference calculates the difference between
+// The SquareOfSums and the SumOfSquares for the
+// first 'num' natural numbers
+func Difference(num int) int {
+	return SquareOfSums(num) - SumOfSquares(num)
+}

go/difference-of-squares/difference_of_squares_test.go

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+package diffsquares
+
+import "testing"
+
+var tests = []struct{ n, sqOfSums, sumOfSq int }{
+	{5, 225, 55},
+	{10, 3025, 385},
+	{100, 25502500, 338350},
+}
+
+func TestSquareOfSums(t *testing.T) {
+	for _, test := range tests {
+		if s := SquareOfSums(test.n); s != test.sqOfSums {
+			t.Fatalf("SquareOfSums(%d) = %d, want %d", test.n, s, test.sqOfSums)
+		}
+	}
+}
+
+func TestSumOfSquares(t *testing.T) {
+	for _, test := range tests {
+		if s := SumOfSquares(test.n); s != test.sumOfSq {
+			t.Fatalf("SumOfSquares(%d) = %d, want %d", test.n, s, test.sumOfSq)
+		}
+	}
+}
+
+func TestDifference(t *testing.T) {
+	for _, test := range tests {
+		want := test.sqOfSums - test.sumOfSq
+		if s := Difference(test.n); s != want {
+			t.Fatalf("Difference(%d) = %d, want %d", test.n, s, want)
+		}
+	}
+}
+
+// Benchmark functions on just a single number (100, from the original PE problem)
+// to avoid overhead of iterating over tests.
+func BenchmarkSquareOfSums(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		SquareOfSums(100)
+	}
+}
+
+func BenchmarkSumOfSquares(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		SumOfSquares(100)
+	}
+}
+
+func BenchmarkDifference(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Difference(100)
+	}
+}