【LeetCode】-Reverse Words in a String

Given an input string, reverse the string word by word.

For example,

Given s = "

the sky is blue

",

return "

blue is sky the

".

Clarification:

What constitutes a word?

A sequence of non-space characters constitutes a word.
Could the input string contain leading or trailing spaces?

Yes. However, your reversed string should not contain leading or trailing spaces.
How about multiple spaces between two words?

Reduce them to a single space in the reversed string.

/*
*解题思路：
*1.去掉字符串收尾的空格，并把单词间的多个空格用一个空格替换掉；
*2.先翻转每个单词，再翻转整个字符串。*/

public class Solution {

private void reverseWord(  char[] arr, int start, int end ){
char temp;
while( start<end ){
temp = arr[start];
arr[start] = arr[end];
arr[end] = temp;
start++;
end--;
}
}

public String reverseWords(String s) {
String str = s.trim().replaceAll("\\s+", " ");
int len = str.length();
char[] arr_str = str.toCharArray();
int start = 0;
int end = 0;
while( start<len ){
end = start;
while( end<len && arr_str[end]!=' ' ){
end++;
}
reverseWord( arr_str, start, end-1 );
start = end+1;
}
reverseWord( arr_str, 0, len-1 );
return new String( arr_str );
}
}