Reverse Words in a String

Problem Given a string of length N, reverse it word by word — the order of the words is reversed, but the characters within each word stay as they are.

Input / Output

• Input: string str, possibly with irregular spacing
• Output: a string with the words in reverse order, separated by exactly one space, with no leading or trailing spaces

Constraints

• Input may contain leading/trailing spaces and multiple consecutive spaces between words
• Output must normalise all whitespace to single spaces
• 1 <= |str| <= 10^4

Example

• Input: " the sky is blue " → Output: "blue is sky the"
• Tricky cases: a string of only spaces " " → ""; a single word "hello" → "hello" unchanged