How hard is LeetCode 186. Reverse Words in a String II?

LeetCode 186. Reverse Words in a String II is rated Medium on LeetCode.

What is the time complexity of LeetCode 186. Reverse Words in a String II?

The Python solution on this page runs in O(n), where n is the length of the character array s.

What is the space complexity of LeetCode 186. Reverse Words in a String II?

The Python solution on this page uses O(1) auxiliary space.

What topics does LeetCode 186. Reverse Words in a String II cover?

LeetCode 186. Reverse Words in a String II is tagged Two Pointers and String on LeetCode.

Is LeetCode 186. Reverse Words in a String II a premium problem?

Yes. LeetCode 186. Reverse Words in a String II is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.

Reverse Words in a String II — LeetCode 186 Python Solution

MediumLeetCode PremiumTwo PointersString

Problem: #186
Pattern: Two Pointers
Reading time: 3 min
Source: leetcode.com

The problem

Given a character array s, reverse the order of the words. A word is defined as a sequence of non-space characters.

Example

Input: s = ["t","h","e"," ","s","k","y"," ","i","s"," ","b","l","u","e"]
Output: ["b","l","u","e"," ","i","s"," ","s","k","y"," ","t","h","e"]

Python solution

Python

class Solution:
    def reverseWords(self, s: List[str]) -> None:
        def reverse(i: int, j: int):
            while i < j:
                s[i], s[j] = s[j], s[i]
                i, j = i + 1, j - 1

        i, n = 0, len(s)
        for j, c in enumerate(s):
            if c == " ":
                reverse(i, j - 1)
                i = j + 1
            elif j == n - 1:
                reverse(i, j)
        reverse(0, n - 1)

Complexity

Measure	Complexity
Time	O(n), where n is the length of the character array s
Space	O(1) auxiliary

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 186. Reverse Words in a String II is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Two Pointers.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 186. Reverse Words in a String II?: LeetCode 186. Reverse Words in a String II is rated Medium on LeetCode.
What is the time complexity of LeetCode 186. Reverse Words in a String II?: The Python solution on this page runs in O(n), where n is the length of the character array s.
What is the space complexity of LeetCode 186. Reverse Words in a String II?: The Python solution on this page uses O(1) auxiliary space.
What topics does LeetCode 186. Reverse Words in a String II cover?: LeetCode 186. Reverse Words in a String II is tagged Two Pointers and String on LeetCode.
Is LeetCode 186. Reverse Words in a String II a premium problem?: Yes. LeetCode 186. Reverse Words in a String II is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.