字符串反转

把一个句子中的单词进行反转，例如“how are you"，进行反转后”you are how“;

策略：1先将整个句子进行反转

2.分别对每个单词进行反转

package com.luo.stringtest;

public class ReverseString {
    public static void main(String[] args) {
        String s = "how are you";
        String returnS = new ReverseString().swapWords(s);
        System.out.println(returnS);
    }
    public String swapWords(String s){
        if(s==null||s.length()==0){
            return null;
        }
        //1.字符串转换为字符数组 chs:how are you
        char[] chars = s.toCharArray();
//        System.out.println("字符串转换成字符数组：");
//        for (char ch:chars){
//            System.out.print(ch);
//        }
//        System.out.println();

        //2.对整个字符串进行字符串反转操作
        swap(chars,0,chars.length-1);

        //3.对单个单词进行反转操作
        int begin = 0;
        for(int i=0;i<chars.length;i++){
            if(chars[i]==' '){
                //以空格为分隔符划分单词，对单个单词进行反转
                swap(chars,begin,i-1);
                begin = i+1;
            }
        }
        //对最后一个单词进行反转
        swap(chars,begin,chars.length-1);
        //利用String的构造函数将字符数组转换成字符串
        return new String(chars);
    }

    private void swap(char[] chars, int front, int end) {
        while (front<end){
            char temp = chars[end];
            chars [end] = chars[front];
            chars[front] = temp;
            front++;
            end--;
        }
//        System.out.println("字符数组反转:");
//        for (char ch:chars){
//            System.out.print(ch);
//        }
//        System.out.println();
    }
}