Syncing

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)