IOI'95 Task: Fence Factory

[ IOI Home page ] Task: Fence Factory

Figure 1: Four fences and some of their letter strings (joints not to scale)

A factory makes a modular fence system. The fence sections are one unit long and may be linked together using a separate joint. A joint always links two sections. Unfortunately, the machine that makes straight joints has broken down. The machine for right-angled (90°) joints still works, and can make left-handed and right-handed joints.

The factory's computer scientist is asked to work out what shapes can be made with right-angled joints only. The computer scientist decides to describe a fence by a string of letters. Each letter tells whether the next section is joined to the left (L) or the right (R).

The string LRL describes a zigzag, consisting of 4 sections (Figure 1a; the joint `cutoff' is greatly exaggerated). The string LLLL describes a closed square (Figure 1b). Some strings describe impossible shapes that intersect themselves, e.g. RLLLL.

From now on we consider only strings describing possible shapes that are closed.

A closed shape can be encoded in several ways, depending on where you start and the direction you go. For example, the strings LLLRLLLR and RLRRRLRR describe the same closed shape (Figure 1c).

Write a program that inputs a string describing a closed shape, and answers the following questions for this shape:

How large is the enclosed area, in square units? Space that can be reached from outside by squeezing in between two joints is not considered enclosed (see Figure 1d: the enclosed area is shaded).
Which strings describe this shape?

Input and Output Data

The input file INPUT.TXT consists of one line containing a single string and nothing else. A string consists of at least 4 and at most 50 letters.

The output file OUTPUT.TXT should consist of at least two lines. On the first line is a single positive integer: the area enclosed by the shape (Subtask A). The next lines each contain a string describing the shape (Subtask B). These strings may be given in any order, but they must all be different.

Figure 2 gives example input and output files corresponding to Figure 1c.

____________   _____________
|__________|   |___________|
|LLLRLLLR  |   |2          |
|__________|   |LLLRLLLR   |
               |LLRLLLRL   |
               |LRLLLRLL   |
               |RLLLRLLL   |
               |RRRLRRRL   |
               |RRLRRRLR   |
               |RLRRRLRR   |
               |LRRRLRRR   |
Figure 2: Example input and output

IOI 95