utf8/reverse/reverse.go

@@ -2,6 +2,32 @@
 
 package reverse
 
+import (
+	"strings"
+	"unicode/utf8"
+)
+
+// inplace []rune reverse with 2 allocations
+// first for runes slice and second for output
+// func Reverse(input string) string {
+// 	runes := []rune(input)
+// 	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
+// 		runes[i], runes[j] = runes[j], runes[i]
+// 	}
+// 	return string(runes)
+// }
+
+// string.Builder and utf8 decoding magic = 1 allocation
+// overall more iterations but each one is faster,
+// so its as fast as the inplace []rune reverse
 func Reverse(input string) string {
-	return ""
+	output := strings.Builder{}
+	output.Grow(len(input))
+	end := len(input)
+	for end > 0 {
+		r, n := utf8.DecodeLastRuneInString(input[:end])
+		end -= n
+		output.WriteRune(r)
+	}
+	return output.String()
 }

utf8/spacecollapse/collapse.go

@@ -2,6 +2,44 @@
 
 package spacecollapse
 
+import (
+	"strings"
+	"unicode"
+)
+
+// 1 alloc/op, best ns/op but more iterations overall
 func CollapseSpaces(input string) string {
-	return ""
+	output := strings.Builder{}
+	output.Grow(len(input))
+	writeSpace := true
+	for _, r := range input {
+		if unicode.IsSpace(r) {
+			if writeSpace {
+				output.WriteRune(' ')
+			}
+			writeSpace = false
+		} else {
+			output.WriteRune(r)
+			writeSpace = true
+		}
+	}
+	return output.String()
 }
+
+// 3 allocs/op for runes slice, output slice and output string
+// func CollapseSpaces(input string) string {
+// 	runes := []rune(input)
+// 	output, writeSpace := make([]rune, 0, len(runes)), true
+// 	for _, r := range input {
+// 		if unicode.IsSpace(r) {
+// 			if writeSpace {
+// 				output = append(output, ' ')
+// 			}
+// 			writeSpace = false
+// 		} else {
+// 			output = append(output, r)
+// 			writeSpace = true
+// 		}
+// 	}
+// 	return string(output)
+// }