The Blocks Problem
Time limit: 3.000 seconds
Background
Many areas of Computer Science use simple, abstract domains for both analytical and empirical studies. For example, an early AI study of planning and robotics (STRIPS) used a block world in which a robot arm performed tasks involving the manipulation of blocks.
In this problem you will model a simple block world under certain rules and constraints. Rather than determine how to achieve a specified state, you will “program” a robotic arm to respond to a limited set of commands.
The Problem
The problem is to parse a series of commands that instruct a robot arm in how to manipulate blocks that lie on a flat table. Initially there arenblocks on the table (numbered from 0 ton-1) with blockbiadjacent to blockbi+1for allas shown in the diagram below:
Figure:Initial Blocks World
The valid commands for the robot arm that manipulates blocks are:
moveaontob
whereaandbare block numbers, puts blockaonto blockbafter returning any blocks that are stacked on top of blocksaandbto their initial positions.
moveaoverb
whereaandbare block numbers, puts blockaonto the top of the stack containing blockb, after returning any blocks that are stacked on top of blockato their initial positions.
pileaontob
whereaandbare block numbers, moves the pile of blocks consisting of blocka, and any blocks that are stacked above blocka, onto blockb. All blocks on top of blockbare moved to their initial positions prior to the pile taking place. The blocks stacked above blockaretain their order when moved.
pileaoverb
whereaandbare block numbers, puts the pile of blocks consisting of blocka, and any blocks that are stacked above blocka, onto the top of the stack containing blockb. The blocks stacked above blockaretain their original order when moved.
quit
terminates manipulations in the block world.
Any command in whicha=bor in whichaandbare in the same stack of blocks is an illegal command. All illegal commands should be ignored and should have no affect on the configuration of blocks.
The Input
The input begins with an integernon a line by itself representing the number of blocks in the block world. You may assume that0 <n< 25.
The number of blocks is followed by a sequence of block commands, one command per line. Your program should process all commands until thequitcommand is encountered.
You may assume that all commands will be of the form specified above. There will be no syntactically incorrect commands.
The Output
The output should consist of the final state of the blocks world. Each original block position numberedi(wherenis the number of blocks) should appear followed immediately by a colon. If there is at least a block on it, the colon must be followed by one space, followed by a list of blocks that appear stacked in that position with each block number separated from other block numbers by a space. Don’t put any trailing spaces on a line.
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