Reverse the fields of a log line

Question

An execution log line has space-separated fields, sometimes with irregular spacing. Reverse the order of the fields and join them with single spaces, dropping any leading, trailing, or repeated spaces.

line = "FILL   100 AAPL"
-> "AAPL 100 FILL"

Return the fields in reverse order, single-spaced. Aim for $O(n)$ .

Accepted Answer

Split on arbitrary runs of whitespace (Python's str.split() with no argument does exactly this and ignores leading and trailing gaps), reverse the resulting list, and rejoin with a single space. Tracing "FILL 100 AAPL": splitting yields ["FILL", "100", "AAPL"], reversing gives ["AAPL", "100", "FILL"], and joining produces "AAPL 100 FILL". Time O(n), space O(n) for the token list. The whitespace normalization is the whole trick: a naive split on the single character " " would keep empty tokens from doubled spaces and mangle the output. Takeaway. Reach for the whitespace-aware split() when fiel…

Reverse the fields of a log line

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