day 161: reverse the bits of a 32-bit integer

day161/problem.go

@@ -0,0 +1,17 @@
+package day161
+
+// Reverse32Bits reverses the bits and returned the result.
+// Runs in O(32) time.
+func Reverse32Bits(num uint32) uint32 {
+	var rev uint32
+	offset := uint(32)
+	for num != 0 {
+		offset--
+		rev <<= 1
+		if num&1 == 1 {
+			rev ^= 1
+		}
+		num >>= 1
+	}
+	return rev << offset
+}

day161/problem_test.go

@@ -0,0 +1,27 @@
+package day161
+
+import "testing"
+
+var testcases = []struct {
+	given, expected uint32
+}{
+	{4042322160, 252645135},
+	{3, 3221225472},
+}
+
+func TestReverse32Bits(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := Reverse32Bits(tc.given); result != tc.expected {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkReverse32Bits(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			Reverse32Bits(tc.given)
+		}
+	}
+}