Most shifty

Don Yang

Judges' comments:

To use:

more generated1.c
more generated2.c
more generated3.c


./left < prog.c
./right < prog.c
./left < prog.c | ./left

./shift < prog.c


Selected Judges Remarks:

Code should be readable in any direction! This tool will help you rotate your code so you don’t have to stare at it sideways or even upside down. Rotating this program left and recompiling will reveal other tools including a right rotate and a shift program.

Strange things happen when the world is upside down! It is entirely possible that this is remark is completely misleading.

What exactly does the shift program do?

Like a great sliding puzzle (hint) this entry has 6 more programs that will reveal messages and one more tool that can be used to reveal the final message hidden in the original source. All of these can be created using combinations of ./left, ./right and ./shift and the additionally generated programs.

The final message can be revealed using

./msg9 < prog.c

But what combinations will generate ./msg3, ./msg4, ./msg5, ./msg6, ./msg7, ./msg8 and finally ./msg9?

Author’s comments:

Tools usage

Nuko is a text rotator: given some text in stdin, Nuko will write the same text to stdout, but rotated 90 degrees counterclockwise.

gcc prog.c -o left
./left < input.txt > rotated_counterclockwise.txt

Due to static memory allocation, only the first 1K columns by 1K rows are rotated, the rest are silently ignored. But fear not, a separate tool with dynamic memory allocation is included:

./left < prog.c > r1.c
gcc r1.c -o right
./right < input.txt > rotated_clockwise.txt

For variety, this second tool rotates clockwise instead of counterclockwise. Also, it can handle files larger than 1024x1024, depending on how much memory you got.

Of course we wouldn’t stop with just two rotations, if we continue to rotate counterclockwise once more, we get another program. This program outputs a single message to stdout, which is the name of the series that Nuko came from.

./left < prog.c | ./left > r2.c
gcc r2.c -o msg0

There is one final rotation, which produces a tool that removes leading whitespaces:

./left < prog.c | ./left | ./left > r3.c
gcc r3.c -o shift
./shift < input.txt > no_leading_space.txt

Where this might be useful, besides ruining the formatting of certain files, is that it completes the set of tools needed to solve the puzzle that is embedded in prog.c

Puzzle box

Notice how the edges of prog.c contain two notches. By rotating prog.c and removing leading space, the code would be shifted one space toward one of those notches (and creating a new notch on the other side). This shifted code behaves slightly different from the original program. For example, here are two more messages that can be produced:

./shift < prog.c | ./right > msg1.c && gcc msg1.c -o msg1 && ./msg1
./shift < prog.c | ./left > msg2.c && gcc msg2.c -o msg2 && ./msg2

In total, there are 9 embedded strings that can be produced via a sequence of rotates and shifts, one of which can be used to extract the 10th final string from prog.c. The intent is to simulate those wooden puzzle boxes that can be opened by pushing and shifting various well-concealed seams. Thus, finding the correct sequence of rotates and shifts is left as an exercise to the reader (but if you are really lazy, just read the Makefile).

Source code for all the tools needed to solve this puzzle are embedded in prog.c, all you need is a C compiler.



Nuko and the rotated tools accepts only ASCII files where each character maps to exactly one byte. Also, end-of-line sequence is assumed to be LF only, as opposed to CR-LF. All control characters are treated like normal printable characters, so files containing tabs will look weird after rotation, for example.

Nuko has been verified to work with these compiler / OS combinations:

Nuko compiles without warnings with all compilers above, even with “-Wall -Wextra -pedantic” for gcc and clang.

Creative Commons License

© Copyright 1984-2018, Leo Broukhis, Simon Cooper, Landon Curt Noll - All rights reserved
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.