Answer Set Programming

The components in the grid can be either connections (straight pipes, corners or T-joints) or computers, that act as end-points. One (and only one) connection plays the role of server (in the figure above, the gray rectangle with green leds). Depending on the scenario, the server can be on a pipe, a corner or a tjoint. The puzzle consists in finding a rotation for each component so that the whole network is connected to the server. Note that all pieces must be used and that there cannot be lose ends in pipe components. You can play Netwalk online here.

For simplicity, we will only consider the problem of finding the right orientation for each component, disregarding the number of rotations required with respect to the initial state.

Input

Since we are not interested in the original orientation of each component, we will use an input file just describing the type of component in each grid cell using a character for each case: c - corner, l - straight line, t - joint and p - PC. When the character is a capital letter (C, L, T or P), it will point out that the server is located in that connection. As an example, the scenario above would be described as:

cpclc
tlcpl
pcctc
cCpcc
clllc

This text file must be translated into ASP facts that will depend on the representation you decide to use.

Output

The output must show, for each cell, the number of clockwise turns (0, 1, 2 or 3) that are required to solve the puzzle, assuming that the 0-position is the following one in each case:

The output will use a predicate rotate(X,Y,N) that means that cell in row X, column Y, must be rotated N times. Optional: you can generate an HTML file showing the graphic output as an array of images, one per each cell.