diff --git a/src/chapter1/problem3.go b/src/chapter1/problem3.go
index 0e1cc5a..cb64116 100644
--- a/src/chapter1/problem3.go
+++ b/src/chapter1/problem3.go
@@ -26,3 +26,27 @@ func URLify(input string) string {
 	}
 	return string(temp)
 }
+
+// Less "real world" version taking a []rune with spaces
+// on the end to be able to URLify in place.
+// O(n), in place.
+func URLifySlice(input []rune) {
+	inWord := false
+	slowPtr := len(input) - 1
+	for i := len(input) - 1; i >= 0; i-- {
+		if input[i] == rune(' ') {
+			if inWord {
+				input[slowPtr-2] = rune('%')
+				input[slowPtr-1] = rune('2')
+				input[slowPtr] = rune('0')
+				slowPtr -= 3
+			}
+		} else {
+			if !inWord {
+				inWord = true
+			}
+			input[slowPtr] = input[i]
+			slowPtr--
+		}
+	}
+}
diff --git a/src/chapter1/problem3_test.go b/src/chapter1/problem3_test.go
index 8256550..5ae2ff4 100644
--- a/src/chapter1/problem3_test.go
+++ b/src/chapter1/problem3_test.go
@@ -1,6 +1,7 @@
 package chapter1
 
 import (
+	"reflect"
 	"testing"
 )
 
@@ -21,3 +22,20 @@ func TestURLify(t *testing.T) {
 		}
 	}
 }
+
+func TestURLifySlice(t *testing.T) {
+	cases := []struct {
+		input    []rune
+		expected []rune
+	}{
+		{[]rune("hello my name is      "), []rune("hello%20my%20name%20is")},
+		{[]rune("hello"), []rune("hello")},
+		{[]rune(" hello my name is        "), []rune("%20hello%20my%20name%20is")},
+	}
+	for _, c := range cases {
+		URLifySlice(c.input)
+		if !reflect.DeepEqual(c.expected, c.input) {
+			t.Fatalf("Expected: %s, actual: %s\n", string(c.expected), string(c.input))
+		}
+	}
+}