151. Reverse Words in a String.md

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.

Solution

小bug很多，面试时候是致命的...

Code

class Solution {
    public String reverseWords(String s) {
        List<String> result = new ArrayList<String>();
        if(s.length()==0)
            return s;
        
        int st = 0;
        while(st<s.length() && s.charAt(st)==' ')
            st++;
        
        int i = st;
        while(i<s.length())
        {
            while(i<s.length() && s.charAt(i)!=' ')
                i++;
            String tmp = s.substring(st,i);
            // 选好st和i之后就不需要replace空格惹！
            // result.add(0,tmp.replace(" ",""));
            result.add(0,tmp);
            st = i;
            while(st<s.length() && s.charAt(st)==' ')
                st++;
            i = st+1;
        }
        return String.join(" ",result);
    }
}