Leetcode – Reverse Words in a String II (Java)

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Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters.

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

For example,
Given s = "the sky is blue",
return "blue is sky the".

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

Analysis

This problem is similar to the rotate array to right by k steps problem. 

There are two steps:

  1. use the space ‘ ‘ to determine the boundary of words. We reverse each subarray separated by space. 

2.  reverse the whole array.

See the following implementation in Java: