Reverse Words in a String
Medium · Strings · Two Pointers · String
Problem
You are given a string s. A word is a maximal run of characters that are not spaces; words are separated by one or more spaces, and s may also start or end with spaces.
Return the words of s in reverse order, joined by exactly one space, with no spaces at the start or the end. The letters inside each word keep their order: only the order of the words changes.
Examples
Input: s = "the sky is blue" Output: "blue is sky the"
Input: s = " hello world " Output: "world hello"
The spaces at the ends are dropped.
Input: s = "a good example" Output: "example good a"
Three spaces between words become one.
Constraints
- 1 <= len(s) <= 10^4
- s holds English letters (upper and lower case), digits and spaces
- s has at least one word
Approaches
- Reverse all, then each word, in place — time O(n), space O(n) in Python (O(1) on a mutable array)
Follow-up
If the string were a mutable character array, could you do it with O(1) extra space? And what if the spacing had to stay exactly as it was, with only the words changing places?
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