本系列導航：劍指offer（第二版）java實現導航帖

面試題58：翻轉單詞順序

題目要求：
輸入一個英文句子，翻轉單詞順序，單詞內字符不翻轉，標點符號和普通字母一樣處理。例如輸入輸入“I am a student.”，則輸出“student. a am I”。

解題思路：
首先字符串整體翻轉，得到“.tneduts a ma I”；然后以空格作為分隔符進行切分，對于切分下來的每一部分再進行翻轉，得到“student. a am I”。

package chapter6;

/**
 * Created with IntelliJ IDEA
 * Author: ryder
 * Date  : 2017/8/17
 * Time  : 16:01
 * Description:翻轉字符串
 **/
public class P284_ReverseWordsInSentence {
    public static String reverse(String str){
        StringBuilder stringBuilder = new StringBuilder(str);
        reverseSubString(stringBuilder,0,stringBuilder.length()-1);
        int start = 0,end = stringBuilder.indexOf(" ");
        while (start<stringBuilder.length()&&end!=-1){
            reverseSubString(stringBuilder,start,end-1);
            start = end+1;
            end = stringBuilder.indexOf(" ",start);
        }
        if(start<stringBuilder.length())
            reverseSubString(stringBuilder,start,stringBuilder.length()-1);
        return stringBuilder.toString();
    }
    //翻轉stringBuilder[start,end]
    public static void reverseSubString(StringBuilder stringBuilder,int start,int end){
        for(int i=start;i<=start+(end-start)/2;i++){
            char temp = stringBuilder.charAt(i);
            stringBuilder.setCharAt(i,stringBuilder.charAt(end-i+start));
            stringBuilder.setCharAt(end-i+start,temp);
        }
    }
    public static void main(String[] args){
        System.out.println(reverse("I am a student."));
    }
}

運行結果

student. a am I