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Programming Enigma Puzzles

7 February 2012

Posted by on **From New Scientist #2743, 16th January 2010** [link]

Joe placed six lettered counters on a 3-by-2 grid as shown, reading ENIGMA anticlockwise, and then he removed the E. Penny then slid the counters around, successively moving them up, down or across into a gap, so that after Joe replaced the E in its original position, the letters read ENIGMA clockwise.

What was the smallest number of counters that Penny needed to move to achieve this?

[enigma1578]

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The following Python code does a depth first search, and finds the solution in 44ms.

Solution:The minimum number of moves is 20.