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”
Note: In the string, each word is separated by single space and there will not be any extra space in the string.

难度: easy

题目：给定字符串，返转字符串中的单词，保留空格和单词顺序。

思路：遍历，返转

Runtime: 11 ms, faster than 50.54% of Java online submissions for Reverse Words in a String III.
Memory Usage: 38.7 MB, less than 96.70% of Java online submissions for Reverse Words in a String III.

class Solution {
    public String reverseWords(String s) {
        s = " " + s + " ";
        StringBuilder result = new StringBuilder();
        int begin = 0, end = 0;
        for (int i = 1; i < s.length() - 1; i++) {
            char c = s.charAt(i);
            if (c != ' ' && s.charAt(i - 1) == ' ') {
                begin = i;
                result.append(s.substring(end + 1, begin));
            }
            if (c != ' ' && s.charAt(i + 1) == ' ') {
                end = i;
                for (int j = end; j >= begin; j--) {
                    result.append(s.charAt(j));
                }
            } 
        }
        
        return result.toString();
    }
}