Syncing

go/current

@@ -1 +0,0 @@
-prime-factors

go/nth-prime/README.md

@@ -0,0 +1,27 @@
+# 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

@@ -0,0 +1,33 @@
+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

@@ -0,0 +1,39 @@
+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)
+	}
+}

go/prime-factors/prime.go

@@ -1,16 +1,19 @@
 package prime
 
-import "fmt"
-
 const testVersion = 2
 
 var sieve []int64
 var iter int
 
 func Factors(num int64) []int64 {
-	fmt.Println("Factors Called on ", num)
-	if num == 1 {
+	if len(sieve) == 0 {
+		sieve = append(sieve, int64(2))
+	}
+	switch num {
+	case 1:
 		return []int64{}
+	case 2:
+		return []int64{2}
 	}
 	for i := range sieve {
 		if sieve[i] == num {
@@ -22,28 +25,26 @@ func Factors(num int64) []int64 {
 			return append([]int64{sieve[i]}, Factors(div)...)
 		}
 	}
+
 	// If we're here, we don't have the prime factors for this number
-	// Add 1 to the highest prime that we have and find the next prime
-	i := int64(2)
-	if len(sieve) > 0 {
-		i = sieve[len(sieve)-1]
-	}
-	fmt.Println("  Looking for a new prime starting at ", i)
-	for ; i <= num; i++ {
+	topPrime := sieve[len(sieve)-1]
+	for i := sieve[0]; i*topPrime <= num; i++ {
+		// Check if i is a prime
 		isPrime := true
 		for j := range sieve {
 			if i%sieve[j] == 0 {
+				// Not a prime
 				isPrime = false
-			}
-			if !isPrime {
 				break
 			}
 		}
 		if isPrime {
+			// Found a new prime
 			sieve = append(sieve, i)
-			// New prime in the sieve, try again
+			// New data, recurse
 			return Factors(num)
 		}
 	}
-	return []int64{}
+	// Is this a prime?
+	return []int64{num}
 }

go/prime-factors/primefactors_test.go

@@ -3,7 +3,6 @@ package prime
 // Return prime factors in increasing order
 
 import (
-	"fmt"
 	"reflect"
 	"testing"
 )
@@ -32,13 +31,7 @@ func TestPrimeFactors(t *testing.T) {
 		t.Fatalf("Found testVersion = %v, want %v", testVersion, targetTestVersion)
 	}
 	for _, test := range tests {
-		fmt.Print("Running Test: ")
-		fmt.Print(test)
-		fmt.Print(" :: ")
 		actual := Factors(test.input)
-		fmt.Print(actual)
-		fmt.Print("  Sieve: ")
-		fmt.Println(sieve)
 		if !reflect.DeepEqual(actual, test.expected) {
 			t.Errorf("prime.Factors(%d) = %v; expected %v",
 				test.input, actual, test.expected)