LeetCode 186. Reverse Words in a String II（反转单词）

原创于 2016-05-25 01:36:04 发布 · 1.8k 阅读

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本文介绍了一种解决LeetCode上字符串反转问题的有效方法——两次反转法。该方法首先将整个字符串反转，然后依次反转每个单词，从而实现按单词反转字符串的效果。此方法空间复杂度为O(1)，符合题目要求的就地操作且不使用额外空间。

原题网址：https://leetcode.com/problems/reverse-words-in-a-string-ii/

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?

方法：两次反转。

public class Solution {
    private void reverse(char[] s, int from, int to) {
        while (from<to) {
            char c = s[from];
            s[from] = s[to];
            s[to] = c;
            from ++;
            to --;
        }
    }
    public void reverseWords(char[] s) {
        int pos = 0;
        for(int i=0; i<=s.length; i++) {
            if (i<s.length && s[i] != ' ') continue;
            reverse(s, pos, i-1);
            pos = i+1;
        }
        reverse(s, 0, s.length-1);
    }
}