Reverse the Word Order in Place

Medium

You get a list of characters chars holding a phrase whose words are separated by exactly one space, with no spaces at the start or the end. A word is an unbroken run of non-space characters. Put the words in reverse order; each word itself still reads the same. Return the list with the words reversed. Try not to build an extra list: rearrange the characters inside chars itself with O(1) memory.

Example 1

chars=['g', 'o', ' ', 'f', 'a', 's', 't'] → ['f', 'a', 's', 't', ' ', 'g', 'o']

The words go and fast swap: the list becomes ['f', 'a', 's', 't', ' ', 'g', 'o'].

Example 2

chars=['A', ' ', 'b', ' ', '7'] → ['7', ' ', 'b', ' ', 'A']

The result is ['7', ' ', 'b', ' ', 'A'].

Example 3

chars=['o', 'k'] → ['o', 'k']

There is only one word, so the list stays the same.

Constraints

1 ≤ len(chars) ≤ 10⁵
Each chars[i] is an English letter, a digit or a space
There is at least one word
No leading or trailing spaces; words are separated by exactly one space

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Topics

Two Pointers String

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Input

chars=['g', 'o', ' ', 'f', 'a', 's', 't']

Expected

['f', 'a', 's', 't', ' ', 'g', 'o']

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