186. (Locked)Reverse Words in a String II

Difficulty: Medium

Frequency: N/A 

Similar to Question [151. Reverse Words in a String], but with the following constraints:

“The input string does not contain leading or trailing spaces and the words are always separated by a single space.”

Could you do it in-place without allocating extra space?


Solution 1:

data structure:



1. reverse the whole string

2. reverse the single word


Runtime: O(n)

Space: O(1)



Rotate an array to the right by k steps in-place without allocating extra space. For instance, with k = 3, the array [0, 1, 2, 3, 4, 5, 6] is rotated to [4, 5, 6, 0, 1, 2, 3].

Things to learn:

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