151. Reverse Words in a String

原创于 2018-12-31 09:53:38 发布 · 114 阅读

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本文介绍了一种算法，用于反转字符串中的单词顺序，同时保持每个单词内的字符顺序不变。该算法首先去除字符串首尾的空白字符，并将多个连续的空格压缩为一个。然后，将字符串按单词分割并反转单词顺序，最后将单词重新连接成字符串。

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https://leetcode.com/problems/reverse-words-in-a-string/

Given an input string, reverse the string word by word.

Example:
Input: "the sky is blue",
Output: "blue is sky the".
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) space.

Solution 1:

    public static String reverseWords(String s) {
        String[] res = s.trim().split("\\s+");
        StringBuilder ans = new StringBuilder();
        for (int i = res.length-1; i >= 0; i--) {
            if (i > 0) ans.append(res[i]).append(" ");
            else ans.append(res[i]);
        }
        return ans.toString();
    }

Solution 2:

public static String reverseWords(String s) {
        String[] res = s.trim().split("\\s+");
        Collections.reverse(Arrays.asList(res));
        return String.join(" ", res);
    }