186 Reverse Words in a String II_186reversewordsinastringii-优快云博客

本文链接：https://blog.youkuaiyun.com/dongbeier/article/details/80298827

本文介绍了一种简单高效的算法，用于翻转字符串中的单词。通过两次翻转操作实现：首先翻转每个单词，然后整体翻转整个字符串。该方法无需额外空间，符合in-place的要求。

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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?

这道题让我们翻转一个字符串中的单词，跟之前那题Reverse Words in a String没有区别，由于之前那道题我们就是用in-place的方法做的，而这道题反而更简化了题目，因为不考虑首尾空格了和单词之间的多空格了，方法还是很简单，先把每个单词翻转一遍，再把整个字符串翻转一遍，或者也可以调换个顺序，先翻转整个字符串，再翻转每个单词

public class ReverseWords2 {
    public String reverseWords2 (String s) {
        int left = 0;
        char[] ch = s.toCharArray();
        for (int i = 0; i <= ch.length; i++) {
            if (i == ch.length || ch[i] == ' ') {
                reverse(ch, left, i - 1);
            }
        }
        reverse(ch, left, s.length() - 1);
        return s;
    }
    
    private void reverse(char[] ch, int left, int right) {
        while (left < right) {
        char t = ch[left];
        ch[left++] = ch[right];
        ch[right--] = t;
        }
    }
}