import java.util.Stack;

public class StringReverse {

  // 使用內置類(StringBuilder或StringBuffer)
  public static String reverse1(String s) {
    // StringBuilder strBuilder = new StringBuilder(s);
    // String ret = strBuilder.reverse().toString();
    StringBuffer strBuf = new StringBuffer(s);
    String ret = strBuf.reverse().toString();
    return ret;
  }

  // 有左到右 拼接字符串
  public static String reverse2(String s) {
    String ret = "";
    for (int i = 0; i < s.length(); ++i) {
      ret = s.charAt(i) + ret;
    }
    return ret;
  }

  // 從右到左 拼接字符串
  public static String reverse3(String s) {
    String ret = "";
    for (int i = s.length() - 1; i >= 0; --i) {
      ret += s.charAt(i);
    }
    return ret;
  }

  public static String reverse4(String s) {
    String ret = "";
    char[] charArr = s.toCharArray();
    int len = charArr.length;
    for (int i = 0; i < len / 2; ++i) {
      char tmp = charArr[i];
      charArr[i] = charArr[len - 1 - i];
      charArr[len - 1 - i] = tmp;
    }
    ret = new String(charArr);
    return ret;
  }

  // 使用異或
  public static String reverse5(String s) {
    String ret = "";
    char[] charArr = s.toCharArray();
    int begin = 0, end = charArr.length - 1;
    while (begin < end) {
      charArr[begin] = (char) (charArr[begin] ^ charArr[end]);
      charArr[end] = (char) (charArr[begin] ^ charArr[end]);
      charArr[begin] = (char) (charArr[begin] ^ charArr[end]);

      begin++;
      end--;
    }
    ret = new String(charArr);
    return ret;
  }

  // 使用棧
  public static String reverse6(String s) {
    String ret = "";
    Stack<Character> stack = new Stack<Character>();
    for (int i = 0; i < s.length(); ++i) {
      stack.push(s.charAt(i));
    }
    while (!stack.isEmpty()) {
      ret += stack.pop();
    }

    return ret;
  }

}