Merge pull request #310 from vaskoz/day148

Day148

Author: vaskoz

README.md

@@ -158,3 +158,4 @@ problems from
 * [Day 145](https://github.com/vaskoz/dailycodingproblem-go/issues/302)
 * [Day 146](https://github.com/vaskoz/dailycodingproblem-go/issues/303)
 * [Day 147](https://github.com/vaskoz/dailycodingproblem-go/issues/304)
+* [Day 148](https://github.com/vaskoz/dailycodingproblem-go/issues/309)

day148/problem.go

@@ -0,0 +1,22 @@
+package day148
+
+import "fmt"
+
+// GrayCodes returns a slice of strings representing the bits of
+// gray codes for the requested number of bits.
+func GrayCodes(bits int) []string {
+	if bits < 1 {
+		return nil
+	} else if bits == 1 {
+		return []string{"0", "1"}
+	}
+	smaller := GrayCodes(bits - 1)
+	result := make([]string, 0, 2*len(smaller))
+	for _, entry := range smaller {
+		result = append(result, fmt.Sprintf("0%s", entry))
+	}
+	for i := range smaller {
+		result = append(result, fmt.Sprintf("1%s", smaller[len(smaller)-1-i]))
+	}
+	return result
+}

day148/problem_test.go

@@ -0,0 +1,34 @@
+package day148
+
+import (
+	"reflect"
+	"testing"
+)
+
+var testcases = []struct {
+	bits  int
+	codes []string
+}{
+	{2, []string{"00", "01", "11", "10"}},
+	{1, []string{"0", "1"}},
+	{0, nil},
+	{-10, nil},
+	{3, []string{"000", "001", "011", "010", "110", "111", "101", "100"}},
+}
+
+func TestGrayCodes(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := GrayCodes(tc.bits); !reflect.DeepEqual(result, tc.codes) {
+			t.Errorf("Expected %v got %v", tc.bits, result)
+		}
+	}
+}
+
+func BenchmarkGrayCodes(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			GrayCodes(tc.bits)
+		}
+	}
+}