每日算法（6）——字符串逆序输出

1、Java函数实现字符串逆序输出的几种方法

（1）使用StringBuffer类中的reverse()方法将字符串逆序；
（2）利用String类中的toCharArray()转换成字符数组，然后逆序输出数组；
（3）利用String类中的toCharArray()转换成字符数组，将数组二分并交换两边的字符；
（4）遍历字符串，从头部开始逐个正序放入字符串中；
（5）利用栈的先入后出的特性实现字符串的逆序；
（6）通过递归实现字符串的逆序。

2、具体代码

package com.peter.algorithm.other;

import org.junit.Test;
import java.util.Stack;

public class StringReverse {
    @Test
    public void test() {
        String originStr = ".trats ot detnaw uoy yhw nosaer eno taht fo kniht pu evig ot tuoba era uoy nehW";
        //String originStr = "。始开要想么什为你想想，候时的弃放要想你当";
        System.out.println(reverseByStringBuffer(originStr));
        System.out.println(reverseByCharArray(originStr));
        System.out.println(reverseBySwapChar(originStr));
        System.out.println(reverseByInsertFront(originStr));
        System.out.println(reverseByStack(originStr));
        System.out.println(reverseByRecursion(originStr));
    }

    public static String reverseByStringBuffer(String originStr) {
        if (originStr == null || originStr.isEmpty()) {
            throw new IllegalArgumentException("Illegal string!");
        }
        StringBuffer stringBuffer = new StringBuffer(originStr);
        return stringBuffer.reverse().toString();
    }

    public static String reverseByCharArray(String originStr) {
        if (originStr == null || originStr.isEmpty()) {
            throw new IllegalArgumentException("Illegal string!");
        }
        StringBuffer stringBuffer = new StringBuffer();
        char[] originChar = originStr.toCharArray();
        for (int i = originChar.length - 1; i >= 0; i--) {
            stringBuffer.append(originChar[i]);
        }
        return stringBuffer.toString();
    }

    public static String reverseBySwapChar(String originStr) {
        if (originStr == null || originStr.isEmpty()) {
            throw new IllegalArgumentException("Illegal string!");
        }
        char[] originChar = originStr.toCharArray();
        int len = originChar.length;
        int middle = len >>> 1;
        for (int i = 0; i < middle; i++) {
            char temp = originChar[i];
            originChar[i] = originChar[len - i - 1];
            originChar[len - i - 1] = temp;
        }
        return new String(originChar);
    }

    public static String reverseByInsertFront(String originStr) {
        if (originStr == null || originStr.isEmpty()) {
            throw new IllegalArgumentException("Illegal string!");
        }
        StringBuffer stringBuffer = new StringBuffer();
        int len = originStr.length();
        for (int i = 0; i < len; i++) {
            stringBuffer.insert(0, originStr.charAt(i));
        }
        return stringBuffer.toString();
    }

    public static String reverseByStack(String originStr) {
        if (originStr == null || originStr.isEmpty()) {
            throw new IllegalArgumentException("Illegal string!");
        }
        StringBuffer stringBuffer = new StringBuffer();
        Stack<Character> stack = new Stack<>();
        int len = originStr.length();
        //入栈
        for (int i = 0; i < len; i++) {
            stack.push(originStr.charAt(i));
        }
        //出栈
        for (int i = 0; i < len; i++) {
            stringBuffer.append(stack.pop());
        }
        return stringBuffer.toString();
    }

    public static String reverseByRecursion(String originStr) {
        if (originStr == null || originStr.isEmpty()) {
            throw new IllegalArgumentException("Illegal string!");
        }
        if (originStr.length() == 1) {
            return originStr;
        }
        int len = originStr.length();
        return reverseByRecursion(originStr.substring(1, len)) + originStr.charAt(0);
    }
}

3、测试结果

origin string	target string
.trats ot detnaw uoy yhw nosaer eno taht fo kniht pu evig ot tuoba era uoy nehW	When you are about to give up think of that one reason why you wanted to start.
。始开要想么什为你想想，候时的弃放要想你当	当你想要放弃的时候，想想你为什么想要开始。