CISRA Puzzle Competition 2007 - Solutions

This is the archive of the 2007 Puzzle Competition. Please visit the current competition site for information about the latest Puzzle Competition.

B.5 Down to Earth

Intuitive Leap: The puzzle is a game of Connect Four.

The puzzle is this:

drop key guava nit out ivy aim tug pal shin pater dug
1312625166476466714457141222775545275?????

The first thing to notice is that there are the same number of characters in the top line as in the bottom. Removing the spaces from the top line gives us this:

dropkeyguavanitoutivyaimtugpalshinpaterdug
1312625166476466714457141222775545275?????

There are several possible approaches now, but trial and error reveals that subtracting the numbers from the letters produces new words (by subtraction, I mean shifting a letter towards the start of the alphabet by an amount equal to the number):

dropkeyguavanitoutivyaimtugpalshinpaterdug -
1312625166476466714457141222775545275?????
connectfourtheninsertthissentenceinto?????

The question marks stop us completing the sentence, but we'll come back to that later. Reading the sentence as an instruction, it tells us to "connect four" then "insert...". But what does "connect four" mean?

The board in a game of Connect Four has seven columns and six rows. That's 42 slots, which matches the number of characters in the puzzle - that's interesting! Connect Four can be played by naming which column (1 to 7) you wish to drop a piece into next. All the numbers from 1 to 7 are present in the puzzle, and 8, 9 and 0 are not present. This is looking hopeful!

If we play the game by dropping pieces according to the sequence of numbers, we can find out what the board will look like. In the diagram below, the pieces of the two players are marked "x" and "o", and a sequence number is written next to each piece. (For example, the 5th move of the game was played by player "x", and is shown as "x 5".)

+--1----2----3----4----5----6----7--+
| x25  x35       x33  x37  o16  o36 |
| x23  o28       o24  o34  x15  o30 |
| o18  x27       o20  o32  x13  x29 |
| o 8  o26       x19  x31  o10  o22 |
| x 3  o 6       o14  x21  x 9  x17 |
| x 1  o 4  o 2  x11  x 7  x 5  o12 |
+--1----2----3----4----5----6----7--+

The only way to continue the game is to drop pieces into column 3, which implies that the next five pieces (o19, x20, o20, x21, o21) must all be dropped in column 3. So, we can replace "?????" with "33333" in the puzzle. The final board position (with player "o" winning on the last move) will be this:

+--1----2----3----4----5----6----7--+
| x25  x35  o42  x33  x37  o16  o36 |
| x23  o28  x41  o24  o34  x15  o30 |
| o18  x27  o40  o20  o32  x13  x29 |
| o 8  o26  x39  x19  x31  o10  o22 |
| x 3  o 6  o38  o14  x21  x 9  x17 |
| x 1  o 4  o 2  x11  x 7  x 5  o12 |
+--1----2----3----4----5----6----7--+

And the missing word is "board":

dropkeyguavanitoutivyaimtugpalshinpaterdug -
131262516647646671445714122277554527533333
connectfourtheninsertthissentenceintoboard

The full instruction can now be read: "connect four then insert this sentence into board". How can we insert that sentence? By dropping letters from that sentence into the board, instead of "x" and "o" pieces. If we do that, we get this result:

+-1-2-3-4-5-6-7-+
| s n d e o i t |
| h n r i i n e |
| S E A R C H t |
| f s o e n u t |
| n c b e t o n |
| c n o r t e t |
+-1-2-3-4-5-6-7-+

The password, SEARCH, can now be seen running across the middle of the board.