Assignment 1 Karel the Robot
背景介绍
Karel 是一个机器人，具有的功能有
move(),turnLeft(),putBeeper(),pickBeeper()等功能。Karel的升级版SuperKarel具有的功能有
frontIsClear(),leftIsClear(),rightIsClear(),beepersPresent(),beepersInBag(),facingNorth(),facingSouth(),facingEast(),facingwest()等功能
题目1：
Your first task is to solve a simple story-problem in Karel’s world. Suppose that Karel
has settled into its house, which is the square area in the center of the following diagram:
Karel starts off in the northwest corner of its house as shown in the diagram. The problem
you need to get Karel to solve is to collect the newspaper—represented (as all objects in
Karel’s world are) by a beeper—from outside the doorway and then to return to its initial
position.
This exercise is extremely simple and exists just to get you started. You can assume that
every part of the world looks just as it does in the diagram. The house is exactly this size,
the door is always in the position shown, and the beeper is just outside the door. Thus, all
you have to do is write the sequen ce of commands necessary to have Karel
- Move to the newspaper,
- Pick it up, and
- Return to its starting point.
Even though the program is only a few lines, it is still worth getting at least a little
practice in decomposition. In your solution, include a private method for each of the
steps shown in the outline.
题目2
Karel has been hired to repair the damag e done to the Quad in the 1989 earthquake. In
particular, Karel is to repair a set of arches where some of the stones (represented by
beepers, of course) are missing from the columns supporting the arches, as follows:
Your program should work on the world shown above, but it shoul d be general enough to
handle any world that meets certa in basic conditions as outlined at the end of this
problem. There are several example worlds in the starter folder, and your program should
work correctly with all of them.
When Karel is done, the missing stones in the columns should be replaced by beepers, so
that the final picture resulting from the world shown above would look like this:
Karel may count on the following facts about the world, list on the next page:
- Karel starts at 1st Avenue and 1st Stre et, facing east, with an infinite number of
beepers. - The columns are exactly four units apart, on 1st, 5th, 9th Avenue, and so forth.
+The end of the columns is marked by a wall immediately after the final column. This
wall section appears a fter 13th Avenue in the example, but your program should work
for any number of columns. - The top of the column is mar ked by a wall, but Karel cannot assume that columns are
always five units high, or even that all columns are the same height. - Some of the corners in the column may already contain beepers representing stones
that are still in place. Your program should not put a second beeper on these corners.
题目3
In this exercise, your job is to get Karel to crea te a checkerboard pattern of beepers inside
an empty rectangular world, as illustrated in the following before-a nd-after diagram:
This problem has a nice decomposition structure along with some interesting algorithmic issues. As you think about how you will solve the problem, you should make sure that
your solution works with checkerboards that are different in size from the standard 8 x 8 checkerboard shown in the example. Odd-sized checkerboards are tricky, and you should make sure that your program generates the following pattern in a 5x3 world:
Another special case you need to consider is that of a world which is only one column
wide or one row high. The starter folder c ontains several sample worlds that test these
special cases, and you should make sure that your program works for each of them.
题目4
As an exercise in solving algorithmic problems, program Karel to place a single beeper at
the center of 1st Street. For example, if Karel starts in the world
it should end with Karel standing on a beeper in the following position:
Note that the final configuration of the world should have only a single beeper at the
midpoint of 1st Street. Along the way, Karel is allowed to place additional beepers
wherever it wants to, but must pick them all up again before it finishes.
In solving this problem, you may count on the following facts about the world:
- Karel starts at 1st Avenue and 1st Stre et, facing east, with an infinite number of
beepers in its bag. - The initial state of the world in cludes no interior walls or beepers.
- The world need not be square, but you may assume that it is at least as tall as it is wide.
Your program, moreover, can assume the following simplifications:
- If the width of the world is odd, Karel must put the beeper in the center square. If the
width is even, Karel may drop the beeper on either of the two center squares. - It does not matter which direction Karel is facing at the end of the run.
There are many different algorithms you can use to solve this problem. The interesting
part of this assignment is to come up with a strategy that works.
问题解答
CollectNewspaperKarel.java
import stanford.karel.*;
public class CollectNewspaperKarel extends SuperKarel {
public void run() {
move();
move();
turnRight();
move();
turnLeft();
move();
pickBeeper();
turnLeft();
turnLeft();
move();
move();
move();
turnRight();
move();
turnRight();
}
}
StoneMasonKarel.java
import stanford.karel.*;
public class StoneMasonKarel extends SuperKarel {
public void run() {
turnLeft();
while(true){//之前写的while(frontIsClear())在column长度为1时会出现错误
fixLine();
}
}
private void fixLine() {
while(frontIsClear()){
if(noBeepersPresent()) {
putBeeper();
}
move();
}
if(facingNorth()) {
turnRight();
if(noBeepersPresent()) {
putBeeper();
}
if(frontIsClear()) {
move4Steps();
turnLeft();
while(frontIsClear()) {
move();
}
turnRight();
turnRight();
}
}else if (facingSouth()){
turnLeft();
if(noBeepersPresent()) {
putBeeper();
}
if(frontIsClear()) {
move4Steps();
turnRight();
while(frontIsClear()) {
move();
}
turnLeft();
turnLeft();
}
}
}
private void move4Steps() {
move();
move();
move();
move();
}
}
CheckerboardKarel.java
import stanford.karel.*;
public class CheckerboardKarel extends SuperKarel {
public void run() {
while(frontIsClear()) {
while(frontIsClear()) {
putBeeper();
if(beepersPresent()) {
move();
}
if(frontIsClear()){
move();
}
}
if(facingEast()) {
if(leftIsClear()){
turnLeft();
if(frontIsClear()) {
move();
}
turnLeft();
}
}else{
if(rightIsClear()){
turnRight();
if(frontIsClear()) {
move();
}
turnRight();
}
}
}
if(facingEast()) {
turnLeft();
while(frontIsClear()) {
putBeeper();
if(beepersPresent()) {
move();
}
if(frontIsClear()){
move();
}
}
}
else{turnRight();
while(frontIsClear()) {
putBeeper();
if(beepersPresent()) {
move();
}
if(frontIsClear()){
move();
}
}
}
if(noBeepersPresent()){
moveBack();
if(beepersPresent()) {
moveBack();
}else{
moveBack();
putBeeper();
}
}
}
private void moveBack() {
turnAround();
move();
}
}