917 finish

Author: aQuaYi

Algorithms/0917.reverse-only-letters/reverse-only-letters.go

@@ -1,6 +1,25 @@
 package problem0917
 
 func reverseOnlyLetters(S string) string {
+	bs := []byte(S)
 
-	return ""
+	left, right := 0, len(bs)-1
+	for left < right {
+		for left < right && !isLetter(bs[left]) {
+			left++
+		}
+		for left < right && !isLetter(bs[right]) {
+			right--
+		}
+		bs[left], bs[right] = bs[right], bs[left]
+		left++
+		right--
+	}
+
+	return string(bs)
+}
+
+func isLetter(b byte) bool {
+	return 'a' <= b && b <= 'z' ||
+		'A' <= b && b <= 'Z'
 }