186. Reverse Words in a String II

题目：

Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters.

The input string does not contain leading or trailing spaces and the words are always separated by a single space.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Could you do it in-place without allocating extra space?

链接：  http://leetcode.com/problems/reverse-words-in-a-string-ii/

6/21/2017

3ms, 39%

注意不要遗漏了最后一个reverse，end都是exclusive的，这样跟其他库函数类似。

public class Solution {
    public void reverseWords(char[] s) {
        if (s == null || s.length == 0) {
            return;
        }
        reverse(s, 0, s.length);
        int start = 0;
        for (int i = 1; i < s.length; i++) {
            if (s[i] == ' ') {
                reverse(s, start, i);
                start = i + 1;
            }
        }
        reverse(s, start, s.length);
        return;
    }
    private void reverse(char[] s, int start, int end) {
        for (int i = start, j = end - 1; i < j; i++, j--) {
            char tmp = s[i];
            s[i] = s[j];
            s[j] = tmp;
        }
        return;
    }
}

更多讨论

https://discuss.leetcode.com/category/194/reverse-words-in-a-string-ii