#151 - Reverse Words in a String

MediumArray / String

Given an input string s, reverse the order of the words. A word is a maximal sequence of non-space characters. The returned string should have a single space between words and no leading/trailing spaces.

Input	Output
s = "the sky is blue"	"blue is sky the"
s = " hello world "	"world hello"
s = "a good example"	"example good a"

Solution Space

Try it

/**
 * Reverses the order of words in a string, collapsing extra spaces.
 *
 * @param s  Input string (may have leading/trailing/multiple spaces)
 * @returns  Words in reverse order separated by single spaces
 */
export function reverseWords(s: string): string {
  const words = s.trim().split(/\s+/);
  return words.reverse().join(" ");
}

Approach: split + reverse – split the string by spaces, filter out empty words, reverse the array of words, and join them with a single space.

Time: O(n) – one pass to split, one to reverse, one to join.

Space: O(n) – storing the words array.

Alternative approaches:

Approach	Idea	Time	Space
In-place reverse (C-style)	Reverse entire char array, then reverse each word individually	O(n)	O(1) (only if mutable char array)
Stack	Push each word, then pop all	O(n)	O(n)

Why split + reverse is preferred:

• Most concise and idiomatic in languages with string utilities.
• Same optimal O(n) time; the in-place approach only matters in languages with mutable strings.

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