/**
 * 
 */
package com.wsheng.aggregator.algorithm.string;

import java.util.Stack;

/**
 * 8 种字符串反转的方法, 其实可以是9种方法，第9种是使用StringBuffer和StringBuilder中实现的方法
 * @author Josh Wang(Sheng)
 * 
 * @email  swang6@ebay.com
 * 
 */
public class StringReverse {

	/**
	 * 二分递归地将后面的字符和前面的字符连接起来。
	 * 
	 * @param s
	 * @return
	 */
	public static String reverse1(String s) {
		int length = s.length();
		if (length <= 1)
			return s;
		String left = s.substring(0, length / 2);
		String right = s.substring(length / 2, length);
		return reverse1(right) + reverse1(left);
	}
	
	/**
	 * 取得当前字符并和之前的字符append起来
	 * @param s
	 * @return
	 */
	public static String reverse2(String s) {
		int length = s.length();
		String reverse = "";
		for (int i=0; i<length; i++)
			reverse = s.charAt(i) + reverse;
		return reverse;
	}
	
	/**
	 * 将字符从后往前的append起来
	 * @param s
	 * @return
	 */
	public static String reverse3(String s) {
		char[] array = s.toCharArray();
		String reverse = "";
		for (int i = array.length - 1; i >= 0; i--) {
			reverse += array[i];
		}
		return reverse;
	}
	
	/**
	 * 和StringBuffer()一样，都用了Java自实现的方法，使用位移来实现
	 * @param s
	 * @return
	 */
	public static String reverse4(String s) {
		return new StringBuilder(s).reverse().toString();
	}
	
	/**
	 * 和StringBuilder()一样，都用了Java自实现的方法，使用位移来实现
	 * @param s
	 * @return
	 */
	public static String reverse5(String s) {
		return new StringBuffer(s).reverse().toString();
	}
	
	/**
	 * 二分交换，将后面的字符和前面对应的那个字符交换
	 * @param s
	 * @return
	 */
	public static String reverse6(String s) {
		char[] array = s.toCharArray();
		int end = s.length() - 1;
		int halfLength = end / 2;
		for (int i = 0; i <= halfLength; i++) {
			char temp = array[i];
			array[i] = array[end-i];
			array[end-i] = temp;
		}
		
		return new String(array);
	}
	
	/**
	 * 原理是使用异或交换字符串
	 * a=a^b; 
	 * b=b^a; 
         * a=b^a;
	 * 
	 * @param s
	 * @return
	 */
	public static String reverse7(String s) {
		char[] array = s.toCharArray();
		  
		  int begin = 0;
		  int end = s.length() - 1;
		  
		  while (begin < end) {
			   array[begin] = (char) (array[begin] ^ array[end]);
			   array[end] = (char) (array[end] ^ array[begin]);
			   array[begin] = (char) (array[end] ^ array[begin]);
			   begin++;
			   end--;
		  }
		  
		  return new String(array);
	}
	
	/**
	 * 基于栈先进后出的原理
	 * 
	 * @param s
	 * @return
	 */
	public static String reverse8(String s) {
		char[] array = s.toCharArray();
		Stack<Character> stack = new Stack<Character>();
		for (int i = 0; i < array.length; i++)
			stack.push(array[i]);

		String reverse = "";
		for (int i = 0; i < array.length; i++)
			reverse += stack.pop();
		  
		return reverse;
	}
	
	public static void main(String[] args) {
		System.out.println(reverse1("Wang Sheng"));
		System.out.println(reverse2("Wang Sheng"));
		System.out.println(reverse3("Wang Sheng"));
		System.out.println(reverse4("Wang Sheng"));
		System.out.println(reverse5("Wang Sheng"));
		System.out.println(reverse6("Wang Sheng"));
		System.out.println(reverse7("Wang Sheng"));
		System.out.println(reverse8("Wang Sheng"));
	}
}

来自：http://josh-persistence.iteye.com/blog/2205772