151. Reverse Words in a String

🟠   🔖  双指针 字符串  🔗 LeetCode

题目

Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

Example 1:

Input: s = "the sky is blue"

Output: "blue is sky the"

Example 2:

Input: s = " hello world "

Output: "world hello"

Explanation: Your reversed string should not contain leading or trailing spaces.

Example 3:

Input: s = "a good example"

Output: "example good a"

Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.

Constraints:

• 1 <= s.length <= 10^4
• s contains English letters (upper-case and lower-case), digits, and spaces ' '.
• There is at least one word in s.

Follow-up: If the string data type is mutable in your language, can you solve it in-place with O(1) extra space?

题目大意

给定一个字符串，逐个翻转字符串中的每个单词。

说明：

• 无空格字符构成一个单词。
• 输入字符串可以在前面或者后面包含多余的空格，但是反转后的字符不能包括。
• 如果两个单词间有多余的空格，将反转后单词间的空格减少到只含一个。

请尝试使用 O(1) 额外空间复杂度的 原地 解法。

解题思路

常规的方式是把 s 按空格 split 成若干单词，然后 reverse 这些单词的顺序，最后把这些单词 join 成句子。但这种方式使用了额外的空间，并不是「原地反转」单词。

正确的做法是，先将整个字符串 s 反转，然后将每个单词分别反转，这样，就实现了原地反转所有单词。

原始字符串： "hello world!"
反转整个字符串： "!dlrow olleh"
分别反转每个单词： "world! hello"

不过由于 JS 中字符串是不可变的，字符串方法不会改变原有字符串的内容，而是返回一个新字符串，所以在 JS 中并不是真正的原地反转。

代码

/**
 * @param {string} s
 * @return {string}
 */
// 非原地反转
var reverseWords = function (s) {
  return s
    .split(" ")
    .reverse()
    .filter((i) => i != "")
    .join(" ");
};

相关题目

相关题目

• 🔒 Reverse Words in a String II

- [🔒 Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii)