ReverseString

Author: Bunlong

strings/2-lower-case/LowerCase.java

@@ -8,13 +8,11 @@ public static void main(String[] args) {
 
   public static String toLowerCase(String str) {
     char[] chars = str.toCharArray();
-
     for (int i = 0; i < chars.length; ++i) {
       if (Character.isLetter(chars[i]) && Character.isUpperCase(chars[i])) {
         chars[i] = Character.toLowerCase(chars[i]);
       }
     }
-
     return new String(chars);
   }
 }

strings/3-reverse/ReverseString.java

@@ -0,0 +1,21 @@
+public class ReverseString {
+  public static void main(String[] args) {
+    System.out.println(reverseString("abc123").equals("321cba"));
+    System.out.println(reverseString("321cba").equals("abc123"));
+  }
+
+  public static String reverseString(String str) {
+    if (str == null || str.isEmpty()) {
+      return str;
+    }
+    char[] reverseStr = str.toCharArray();
+    for (int i = 0, j = str.length() - 1; i < j; i++, j--) {
+      char temp = reverseStr[i];
+      reverseStr[i] = reverseStr[j];
+      reverseStr[j] = temp;
+    }
+    return new String(reverseStr);
+  }
+}
+
+// java ReverseString.java