leetcode [151]Reverse Words in a String

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

 

Example 1:

Input: "the sky is blue"
Output: "blue is sky the"

Example 2:

Input: "  hello world!  "
Output: "world! hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: "a good   example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

 

Note:

• A word is defined as a sequence of non-space characters.
• Input string may contain leading or trailing spaces. However, your reversed string should not contain leading or trailing spaces.
• You need to reduce multiple spaces between two words to a single space in the reversed string.

 

Follow up:

For C programmers, try to solve it in-place in O(1) extra space.

题目大意：

给定一个字符串，将字符串中的各个单词进行翻转。单词中可能会有前导和后导空格，去除前导和后导空格，并且将字符串中多个空格转化为一个空格。

解法：

先将整个字符串进行翻转，再将其中以空格为分割的单词，一个一个进行翻转。注意特殊的情况，比如“    ”全为空格的字符串。 

java:

class Solution {
    public String reverseWords(String s) {
        if(s.isEmpty()) return s;
        String reverse=new StringBuilder(s).reverse().toString();
        System.out.println(reverse);
        StringBuilder res=new StringBuilder();
        int i=0;
        while(i<reverse.length()){
            StringBuilder tmp=new StringBuilder();
            while(i<reverse.length()&&reverse.charAt(i)==' ') i++;
            if(i<reverse.length()) res.append(' ');
            while(i<reverse.length()&&reverse.charAt(i)!=' ') tmp.append(reverse.charAt(i++));
            if(tmp.length()>0) res.append(tmp.reverse());
        }

        return res.length()==0?"":res.toString().substring(1);
    }
}