alumni

Stanford Engineering Puzzle

January 2007

Sometimes it is not enough for a kidney patient to find a willing donor. If a donor and the intended recipient are incompatible, the next step for doctors is to try to find a donor-recipient pair that is compatible with the first pair. Then they could swap. But given several such pairs, there is a way to maximize the number of possible donations. Anything less would deny someone a lifesaving new kidney.

Alumna Sommer Gentry, a professor of applied mathematics at the U.S. Naval Academy, and her transplant surgeon husband are tackling this problem by creating a system called Optimized Match that can analyze donation pairs and find the maximum number of matches among them.

Directions for puzzle

In this new version of the puzzle we introduced last month, your goal is still to find the maximum and minimum number of possible matches between patient-donor pairs. Click on lines to select matches and think carefully about the implications of each move. Each pair can be a potential party to many matches, but can only be involved in one actual match. When you successfully maximize and then minimize the matches, a "secret word" will be revealed. For fun we will post (below) the names of ten alumni who successfully complete the puzzle and e-mail the secret word in the subject line to staff member Marge Kastner. She'll post entry number 1, 11, 21, 31, 41, etc. up to 91.

You must have Flash installed to run this puzzle, which was designed by Scott Kim of Shufflebrain and programmed by Larry Doyle of Cyberiandesign.

Only three Mind Readers this month, Michael Connors, Robert Barbieri, and Viren Bhanot (again).

Of those who waited until the E-News was sent out, here are the lucky ones whose answers came in at "the right time."

"Winning" entries

  • 1) David Bauman
  • 11) Linda Knudsen
  • 21) Wade Powell
  • 31) Jason Wolfe
  • 41) David Havelin
  • 51) Trevor Lofthouse
  • 61) Charlie Jackson
  • 71) Rohan Chandran
  • 81) James Muldrow
  • 91) Allan Ronne
  • 101) Samantha Infeld
  • 111) Kevin Koehler
  • 121) Seungbeom Kim

We'll list every 10th solver, as long as the answers keep coming in. So if you haven't solved it yet, keep working on it. There's still the chance for fame and glory.

Do you want to try your hand at past puzzles, go to our Archive page.