This is the competition I was thinking of. I must have read it in a dead-image PDF version some other time on HN. This paper isn't the one I recall but the solution is exactly the sort I vaguely recalled.

I'm trying to copy-in the program as it might have existed, with some obvious updates to work in today's shells ...

  #!/bin/sh
  tr -cs A-Za-z '
  ' "${2:-/dev/stdin}" |\
  tr A-Z a-z |\
  sort |\
  uniq -c |\
  sort -rn |\
  sed ${1:-100}q

Alternately (escapes not yet tested) $ tr -cs A-Za-z \012 "${INPUTFILEHERE:-/dev/stdin}" | tr A-Z a-z | sort | uniq -c | sort -rn | sed ${MAXWORDSHERE:-100}q

Edited: Removed some errors likely induced by OCR / me not catching that in the initial transcription from the browser view of the file.

Just to be clear, it was not a competition. For more, please follow the links from some of the previous HN discussions, e.g. https://news.ycombinator.com/item?id=31301777.

[For those who may not follow all the links: Bentley asked Knuth to write a program in Pascal (WEB) to illustrate literate programming—i.e. explaining a long complicated program—and so Knuth wrote a beautiful program with a custom data structure (hash-packed tries). Bentley then asked McIlroy to review the program. In the second half of the review, McIlroy (the inventor of Unix pipes) questioned the problem itself (the idea of writing a program for scratch), and used the opportunity to evangelize Unix and Unix pipes (at the time not widely known or available).]