How can I reverse words in a string efficiently?

Use the two-pointer technique to reverse each word in place without extra space.

What is the time complexity of reversing words in a string?

The time complexity is O(N), where N is the length of the string, as we only traverse the string once.

What if the string contains multiple spaces between words?

Ensure you handle word boundaries by checking spaces between words, ensuring each word is reversed correctly.

Why is the space complexity O(1)?

We reverse the words in place, without using any additional space beyond the input string.

What is the two-pointer approach in this problem?

The two-pointer approach uses one pointer to mark the beginning and another for the end of a word. By swapping characters, the word is reversed in place.

#557

Easy

auto_awesome双·指针·invariant

LeetCode 题解工作台

反转字符串中的单词 III

给定一个字符串 s ，你需要反转字符串中每个单词的字符顺序，同时仍保留空格和单词的初始顺序。示例 1：输入： s = "Let's take LeetCode contest" 输出： "s'teL ekat edoCteeL tsetnoc" 示例 2: 输入： s = "Mr Ding" 输…

双指针字符串

题目描述

给定一个字符串 s ，你需要反转字符串中每个单词的字符顺序，同时仍保留空格和单词的初始顺序。

示例 1：

输入：s = "Let's take LeetCode contest"
输出："s'teL ekat edoCteeL tsetnoc"

示例 2:

输入： s = "Mr Ding"
输出："rM gniD"

提示：

1 <= s.length <= 5 * 10⁴
s 包含可打印的 ASCII 字符。
s 不包含任何开头或结尾空格。
s 里至少有一个词。
s 中的所有单词都用一个空格隔开。

lightbulb

解题思路

方法一：模拟

我们可以将字符串 $\textit{s}$ 按照空格分割成单词数组 $\textit{words}$ ，然后将每个单词反转后再拼接成字符串。

时间复杂度 $O(n)$ ，空间复杂度 $O(n)$ 。其中 $n$ 为字符串 $\textit{s}$ 的长度。

1

2

3

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class Solution:
    def reverseWords(self, s: str) -> str:
        return " ".join(t[::-1] for t in s.split())

speed

复杂度分析

指标	值
时间	\mathcal{O}(N)
空间	\mathcal{O}(1)

psychology

面试官常问的追问

外企场景

question_mark
Look for understanding of two-pointer techniques and their application in string manipulation.
question_mark
Evaluate the candidate's ability to optimize space usage with in-place operations.
question_mark
Test for edge case handling, such as a single-word string or a string with multiple spaces.

warning

常见陷阱

外企场景

error
Misidentifying word boundaries and reversing characters across spaces.
error
Not handling strings with a single word or very short input correctly.
error
Forgetting to manage the space complexity by using in-place modification.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Handle strings with multiple spaces between words or trailing spaces.
arrow_right_alt
Implement the solution with a different space-time trade-off (e.g., using a stack).
arrow_right_alt
Expand the problem to reverse a sentence as a whole while reversing words.

help

常见问题

外企场景

继续练习

#556 下一个更大元素 III #567 字符串的排列 #541 反转字符串 II