String character changes (case insensitive) - Go

Question

I saw this question on one of the socials, presented as an Apple interview question. I have had to paraphrase as it was not given in text format. (Credit: Instagram @greghogg5)

Given a string (S) which is guaranteed to contain only uppercase and lowercase alpha characters, return the number of times that the character changes, not considering case; i.e. "aAa" -> 0, "aBbA" -> 2

Here is my Go code:

strchange.go

package strchange import ( "bytes" ) func CountStringChange(str string) int { var ( count int cur rune ) arr := bytes.Runes([]byte(str)) for i := 0; i < len(arr)-1; i++ { cur = arr[i] // Upper- and lowercase characters are 0x20 bits apart in ASCII if cur&^0x20 != arr[i+1]&^0x20 { count++ } } return count } 

and my test cases:

strchange_test.go

package strchange import ( "fmt" "testing" ) func TestStrChange(t *testing.T) { cases := []struct { str string expected int }{ {"aaa", 0}, {"aAa", 0}, {"aaAAbBbb", 1}, {"abba", 2}, {"abBa", 2}, {"abbba", 2}, {"abBba", 2}, {"aBbBcCcA", 3}, {"aAaBbBcCcAaA", 3}, } for _, c := range cases { actual := CountStringChange(c.str) fmt.Printf("string: %s\t expected: %d actual: %d\n", c.str, c.expected, actual) if c.expected != actual { t.FailNow() } } } 

Answer 1

A few comments.

Simple is good.

strchange.go:

package strchange // s consists of only upper case and lower case English letters. func CountChanges(s string) int { c := 0 for i := 1; i < len(s); i++ { // to lowercase is not equal if s[i]&^0x20 != s[i-1]&^0x20 { c++ } } return c } 

Conforming to standards is good.

Go Wiki: Go Code Review Comments: Useful Test Failures

Benchmarks are a good check on performance.

strchange_test.go:

package strchange import "testing" var changeTests = []struct { s string want int }{ {"aaa", 0}, {"aAa", 0}, {"aaAAbBbb", 1}, {"abba", 2}, {"abBa", 2}, {"abbba", 2}, {"abBba", 2}, {"aBbBcCcA", 3}, {"aAaBbBcCcAaA", 3}, } func TestChanges(t *testing.T) { for _, tt := range changeTests { got := CountChanges(tt.s) if got != tt.want { t.Errorf( "string: %q got: %d want: %d\n", tt.s, got, tt.want, ) } } } func BenchmarkChanges(b *testing.B) { for range b.N { for _, tt := range changeTests { _ = CountChanges(tt.s) } } } 

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$ go test strchange.go strchange_test.go -run=! -bench=. -benchmem BenchmarkChanges-12 51221613 23.41 ns/op 0 B/op 0 allocs/op 

Your code is less performant.

BenchmarkStrChange-12 3787999 323.8 ns/op 224 B/op 9 allocs/op