一道面试题想到的设计模式(观察者模式)
一道面试题想到的。。
面试题：
A?? squad?? of?? robotic?? rovers?? are?? to?? be?? landed?? by?? NASA?? on?? a?? plateau?? on?? Mars.?? ? This?? plateau,?? which?? is?? curiously?? rectangular,?? must?? be?? navigated?? by?? the?? ? rovers?? so?? that?? their?? on-board?? cameras?? can?? get?? a?? complete?? view?? of?? the?? ? surrounding?? terrain?? to?? send?? back?? to?? Earth.?? ? A?? rover's?? position?? and?? location?? is?? represented?? by?? a?? combination?? of?? x?? and?? y?? ? co-ordinates?? and?? a?? letter?? representing?? one?? of?? the?? four?? cardinal?? compass?? ? points.?? The?? plateau?? is?? divided?? up?? into?? a?? grid?? to?? simplify?? navigation.?? An?? ? example?? position?? might?? be?? 0,?? 0,?? N,?? which?? means?? the?? rover?? is?? in?? the?? bottom?? ? left?? corner?? and?? facing?? North.?? ? In?? order?? to?? control?? a?? rover,?? NASA?? sends?? a?? simple?? string?? of?? letters.?? The?? ? possible?? letters?? are?? 'L',?? 'R'?? and?? 'M'.?? 'L'?? and?? 'R'?? makes?? the?? rover?? spin?? 90?? ? degrees?? left?? or?? right?? respectively,?? without?? moving?? from?? its?? current?? spot.?? ? 'M'?? means?? move?? forward?? one?? grid?? point,?? and?? maintain?? the?? same?? heading.?? ? Assume?? that?? the?? square?? directly?? North?? from?? (x,?? y)?? is?? (x,?? y+1).?? ??? ? INPUT:?? ? The?? first?? line?? of?? input?? is?? the?? upper-right?? coordinates?? of?? the?? plateau,?? the?? ? lower-left?? coordinates?? are?? assumed?? to?? be?? 0,0.?? ? The?? rest?? of?? the?? input?? is?? information?? pertaining?? to?? the?? rovers?? that?? have?? ? been?? deployed.?? Each?? rover?? has?? two?? lines?? of?? input.?? The?? first?? line?? gives?? the?? ? rover's?? position,?? and?? the?? second?? line?? is?? a?? series?? of?? instructions?? telling?? ? the?? rover?? how?? to?? explore?? the?? plateau.?? ? The?? position?? is?? made?? up?? of?? two?? integers?? and?? a?? letter?? separated?? by?? spaces,?? ? corresponding?? to?? the?? x?? and?? y?? co-ordinates?? and?? the?? rover's?? orientation.?? ??? ? Each?? rover?? will?? be?? finished?? sequentially,?? which?? means?? that?? the?? second?? rover?? ? won't?? start?? to?? move?? until?? the?? first?? one?? has?? finished?? moving.?? ??? ??? ? OUTPUT?? ? The?? output?? for?? each?? rover?? should?? be?? its?? final?? co-ordinates?? and?? heading.?? ??? ? INPUT?? AND?? OUTPUT?? ??? ? Test?? Input:?? ? 5?? 5?? ? 1?? 2?? N?? ? LMLMLMLMM?? ? 3?? 3?? E?? ? MMRMMRMRRM?? ? 火星探测器?? ? 一小队机器人探测器将由NASA送上火星高原，探测器将在这个奇特的矩形高原上行驶。?? ? 用它们携带的照相机将周围的全景地势图发回到地球。每个探测器的方向和位置将由一个x,y系坐标图和一个表示地理方向的字母表示出来。为了方便导航，平原将被划分为网格状。位置坐标示例：0，0，N，表示探测器在坐标图的左下角，且面朝北方。为控制探测器，NASA会传送一串简单的字母。可能传送的字母为：'L','R'和'M'。?? 'L',和'R'分别表示使探测器向左、向右旋转90度，但不离开他所在地点。'M'?? 表示向前开进一个网格的距离，且保持方向不变。假设以广场（高原）的直北方向为y轴的指向。?? ? 输入：首先输入的line是坐标图的右上方，假定左下方顶点的坐标为0，0。剩下的要输入的是被分布好的探测器的信息。每个探测器需要输入wo?? lines。第一条line?? 提供探测器的位置，第二条是关于这个探测器怎样进行高原探测的一系列说明。位置是由两个整数和一个区分方向的字母组成，对应了探测器的（x,y）坐标和方向。每个探测器的移动将按序完成，即后一个探测器不能在前一个探测器完成移动之前开始移动。?? ? 输出：每个探测器的输出应该为它行进到的最终位置坐标和方向。输入和输出?? 测试如下：???? ??? ? 期待的输入:5?? 5???? 1?? 2?? N?? LMLMLMLMM?? 3?? 3?? E?? MMRMMRMRRM?? 期待的输出?? ? 1?? 3?? N?? 5?? 1?? E?
设计采用观察者模式，如下：
1.被观察者SubjcetNASA.java
?
package cn.zhangzq.obserer;public class Client {/** * @param args */public static void main(String[] args) {Rover rover1=new Rover(3,3,'E');SubjcetNASA testSubjet=new SubjcetNASA();testSubjet.addObserver(rover1);String commandLine="3 3 E MMRMMRMRRM";testSubjet.sendCommand(commandLine);}}?
2观察者Rover.java
?
package cn.zhangzq.obserer;import java.util.Observable;import java.util.Observer;public class Rover implements Observer {private static int coordinateX;private static int coordinateY;private char direction;public Rover(int coordinateX, int coordinateY, char direction) {super();this.coordinateX = coordinateX;this.coordinateY = coordinateY;this.direction = direction;}public void update(Observable o, Object arg) {// 1.解析命令String[] command = parseCommand(o);if ("Y".equals(command[0])) {move(command[1]);diaPlayRovers();}}private void move(String behavior) {for (int i = 0; i < behavior.length(); i++) {char temp = behavior.charAt(i);parseBehavior(temp);}}private void parseBehavior(char temp) {switch (temp) {case 'L':turnLeft();break;case 'R':turnRight();break;case 'M':moveStep();break;}}private void turnRight() {switch (this.direction) {case 'N':this.direction = 'E';break;case 'W':this.direction = 'N';break;case 'S':this.direction = 'W';break;case 'E':this.direction = 'S';break;}}private void moveStep() {if (this.direction == 'S') {coordinateY--;}if (this.direction == 'W') {coordinateX--;}if (this.direction == 'N') {coordinateY++;}if (this.direction == 'E') {coordinateX++;}}private void turnLeft() {switch (this.direction) {case 'N':this.direction = 'W';break;case 'W':this.direction = 'S';break;case 'S':this.direction = 'E';break;case 'E':this.direction = 'N';break;}}/** * * @return [0]:是否接收命令 "Y":接收 ，"N":不接收 ； [1]:具体指令 */@SuppressWarnings("static-access")private String[] parseCommand(Observable o) {String commandLine = ((SubjcetNASA) o).getCommandLine();String[] command = { "", "" };String[] temp = commandLine.split(" ");if (Integer.parseInt(temp[0]) == coordinateX&& Integer.parseInt(temp[1]) == coordinateY&& temp[2].charAt(0) == direction) {command[0] = "Y";} else {command[0] = "N";}command[1] = temp[3];return command;}private void diaPlayRovers() {System.out.println(coordinateX + " " + coordinateY + " " + direction);}}?
?
3.Client.java
?
package cn.zhangzq.obserer;public class Client {/** * @param args */public static void main(String[] args) {Rover rover1=new Rover(3,3,'E');SubjcetNASA testSubjet=new SubjcetNASA();testSubjet.addObserver(rover1);String commandLine="3 3 E MMRMMRMRRM";testSubjet.sendCommand(commandLine);}}?
我这个实现并没有完全按照面试题的要求去做，只是模拟了一下。
1 楼 niwtsew 2008-09-09 敢问楼上的通过了没有，呵呵？有兴趣可以交流一下？