Java Coding 13 - 反转字符串中单词的位置

需求：

反转字符串中单词的位置

例如： i love testing

反转位置后：testing love i

思路：

有很多解决思路，字符串转换成数组，再反向输出数组元素。这里我们介绍类似《Java Coding 12 - 反转字符串中的每个单词》反向遍历字符串，找到空格，空格后字符就是第一个单词的起始位置，结束位置是字符串结束位置。第二个单词起始位置是第二个空格后字符的位置，结束位置是第一个空格前的字符位置，依次类推。。。。最后一个单词的起始位置是0.

实现：

public static String reversePositionOfWordsInString(String str){
        int len = str.length();
        String revertedStr = "";
        int wordEndIndex = len - 1;
        int wordStartIndex;
        for(int i = len -1; i >= 0; i--){
            if(str.charAt(i) == ' ' || i == 0){
                if(i == 0){
                    wordStartIndex = i;
                }else{
                    wordStartIndex = i + 1;
                }
                for(int j = wordStartIndex; j<= wordEndIndex; j++){
                    revertedStr = revertedStr + str.charAt(j);
                }
                revertedStr = revertedStr + " ";
                wordEndIndex = i - 1;
            }
        }
        return revertedStr;
    }
           

完整代码：

import java.util.*;

public class Test {

    public static void main(String[] args) {
        testReversePositionOfWordsInString();
    }
    public static void testReversePositionOfWordsInString(){
        System.out.println("please enter a string, input quit means to exit");
        Scanner in = new Scanner(System.in);
        String str = in.nextLine();
        while(!str.equals("quit")){
            System.out.println("after reverse the position of words in the string " + str);
            System.out.println(reversePositionOfWordsInString(str));
            System.out.println("please enter a string again, input quit means to exit");
            str = in.nextLine();
        }
    }

    public static String reversePositionOfWordsInString(String str){
        int len = str.length();
        String revertedStr = "";
        int wordEndIndex = len - 1;
        int wordStartIndex;
        for(int i = len -1; i >= 0; i--){
            if(str.charAt(i) == ' ' || i == 0){
                if(i == 0){
                    wordStartIndex = i;
                }else{
                    wordStartIndex = i + 1;
                }
                for(int j = wordStartIndex; j<= wordEndIndex; j++){
                    revertedStr = revertedStr + str.charAt(j);
                }
                revertedStr = revertedStr + " ";
                wordEndIndex = i - 1;
            }
        }
        return revertedStr;
    }
    
}