问题：

Given a string, you need to reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example 1:

Input: "Let's take LeetCode contest"Output: "s'teL ekat edoCteeL tsetnoc"。

解决：

① 使用StringBuilder执行，实现非常方便，但是耗时长。

public class Solution {//20ms

    public String reverseWords(String s) {         if(s == null) return null;         StringBuilder sb = new StringBuilder();         String[] schar = s.split(" ");         for (String sc : schar) {             for (int i = sc.length() - 1;i >= 0 ;i -- ) {                 sb.append(sc.charAt(i));             }             sb.append(" ");         }         sb.deleteCharAt(sb.length() - 1);         return sb.toString();     } }

进化版：

public class Solution {//14 ms

    public String reverseWords(String s) {         String[] words = s.split(" ");         StringBuilder sb = new StringBuilder();         boolean isFirst = true;         for(String word : words){             StringBuilder temp = new StringBuilder(word);             word = temp.reverse().toString();             if(isFirst){                 sb.append(word);                 isFirst = false;             }else{                 sb.append(" " + word);             }         }         return sb.toString();     } }

② 全部用数组实现：

public class Solution {//6ms

    public String reverseWords(String s) {         char[] schar = s.toCharArray();         int start = 0;         int end;         while((end = s.indexOf(' ',start)) != -1){             reverse(schar,start,end - 1);             start = end + 1;         }         reverse(schar,start,schar.length - 1);         return new String(schar);     }     public void reverse(char[] arr,int start,int end){         while(start <= end){             char tmp = arr[start];             arr[start] = arr[end];             arr[end] = tmp;             start ++;             end --;         }     } }