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go/nth-prime/README.md

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+# Nth Prime
+
+Write a program that can tell you what the nth prime is.
+
+By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that
+the 6th prime is 13.
+
+If your language provides methods in the standard library to deal with prime
+numbers, pretend they don't exist and implement them yourself.
+
+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://exercism.io/languages/go).
+
+## Source
+
+A variation on Problem 7 at Project Euler [http://projecteuler.net/problem=7](http://projecteuler.net/problem=7)
+
+## Submitting Incomplete Problems
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+

go/nth-prime/nth_prime.go

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+package prime
+
+var sieve []int
+
+func Nth(n int) (int, bool) {
+	if len(sieve) == 0 {
+		sieve = append(sieve, 0)
+		sieve = append(sieve, 2)
+	}
+	if n == 0 {
+		return 0, false
+	}
+
+	for i := sieve[len(sieve)-1]; n <= len(sieve); i++ {
+		// Check if i is a prime
+		isPrime := true
+		for j := 1; j < len(sieve); j++ {
+			if i%sieve[j] == 0 {
+				// Not a prime
+				isPrime = false
+				break
+			}
+		}
+		if isPrime {
+			// Found a new prime
+			sieve = append(sieve, i)
+			if len(sieve) >= n {
+				break
+			}
+		}
+	}
+	return sieve[n], true
+}

go/nth-prime/nth_prime_test.go

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+package prime
+
+import "testing"
+
+var tests = []struct {
+	n  int
+	p  int
+	ok bool
+}{
+	{1, 2, true},
+	{2, 3, true},
+	{3, 5, true},
+	{4, 7, true},
+	{5, 11, true},
+	{6, 13, true},
+	{10001, 104743, true},
+	{0, 0, false},
+}
+
+func TestNth(t *testing.T) {
+	for _, test := range tests {
+		switch p, ok := Nth(test.n); {
+		case !ok:
+			if test.ok {
+				t.Fatalf("Nth(%d) returned !ok.  Expecting ok.", test.n)
+			}
+		case !test.ok:
+			t.Fatalf("Nth(%d) = %d, ok = %t.  Expecting !ok.", test.n, p, ok)
+		case p != test.p:
+			t.Fatalf("Nth(%d) = %d, want %d.", test.n, p, test.p)
+		}
+	}
+}
+
+func BenchmarkNth(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Nth(10001)
+	}
+}