# Vincent.Chan‘s Blog

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### Problem Statement

A simple line drawing program uses a blank 20 x 20 pixel canvas and a directional cursor that starts at the upper left corner pointing straight down. The upper left corner of the canvas is at (0, 0) and the lower right corner is at (19, 19). You are given a String[], commands, each element of which contains one of two possible commands. A command of the form "FORWARD x" means that the cursor should move forward by x pixels. Each pixel on its path, including the start and end points, is painted black. The only other command is "LEFT", which means that the cursor should change its direction by 90 degrees counterclockwise. So, if the cursor is initially pointing straight down and it receives a single "LEFT" command, it will end up pointing straight to the right. Execute all the commands in order and return the resulting 20 x 20 pixel canvas as a String[] where character j of element i represents the pixel at (i, j). Black pixels should be represented as uppercase 'X' characters and blank pixels should be represented as '.' characters.

### Definition

 Class: DrawLines Method: execute Parameters: String[] Returns: String[] Method signature: String[] execute(String[] commands) (be sure your method is public)

1public class DrawLines
2{
3  class Pos
4  {
5    private int X;
6    private int Y;
7    private String status = ".";
8
9    public Pos(int x,int y)
10    {
11      this.X = x;
12      this.Y = y;
13      this.status = ".";
14    }

15
16    public int getX()
17    {
18      return X;
19    }

20
21    public int getY()
22    {
23      return Y;
24    }

25
26    public void setX(int x)
27    {
28      this.X = x;
29    }

30
31    public void setY(int y)
32    {
33      this.Y = y;
34    }

35
36    public void setStatus(String s)
37    {
38      this.status = s;
39    }

40
41    public String getSatus()
42    {
43      return status;
44    }

45
46    public void showPos()
47    {
48      String xStr=X+"";
49      String yStr=Y+"";
50
51      if(X<10)
52      {
53        xStr = "0"+xStr;
54      }

55
56      if(Y<10)
57      {
58        yStr = "0"+yStr;
59      }

60    }

61  }

62
63  public int min = 0, max = 19;
64  public int North = 1, South = 3, West = 2, East = 0;
65  public String LEFT = "LEFT", FORWARD = "FORWARD";
66  public Pos[][] map = null;
67
68
69
70  public DrawLines()
71 {
72   this.direction = South;
73   pos = new Pos(0,0);
74
75   //走之前初始化地图.
76   map = new Pos[max + 1][max + 1];
77   for(int row = 0;row<=max;row++)
78   {
79     for(int col=0;col<=max;col++)
80     {
81       map[row][col] = new Pos(row,col);
82     }

83   }

84 }

85
86  public void showMap()
87  {for (int col = 0; col <= max; col++)
88
89    {
90      for (int row = 0; row <= max; row++)
91      {
92        System.out.print(map[row][col].getSatus());
93      }

94      System.out.println();
95    }

96  }

97
98  private Pos pos = null;
99  private int direction = South;
100
101  public Pos getPos()
102  {
103    return pos;
104  }

105  public void setPos(Pos pos)
106  {
107    this.pos = pos;
108  }

109  /**
110   *
111   * @param cmd
112   */

113  public void execute(String cmd)
114  {
115    if (cmd.equals("LEFT"))
116    {
117      Left();
118    }

119    else if (cmd.indexOf(FORWARD) >= 0)
120    {
121      int from = cmd.indexOf(FORWARD);
122      String stepStr = cmd.substring(from + FORWARD.length());
123      stepStr = stepStr.trim();
124      int step = Integer.parseInt(stepStr);
125      forward(step);
126    }

127    else
128    {
129      System.out.println("未知的命令,无法执行.");
130    }

131  }

132
133  public String[] execute(String[] cmds)
134  {
135    if (cmds != null)
136    {
137      for (int i = 0; i < cmds.length; i++)
138      {
139        execute(cmds[i]);
140      }

141    }

142
143    String[] rval = new String[20];
144    String tempStr = "";
145    for (int col = 0; col <= max; col++)
146     {
147       tempStr = "";
148       for (int row = 0; row <= max; row++)
149       {
150          tempStr = tempStr + map[row][col].getSatus();
151       }

152        rval[col]=tempStr;
153     }

154     return rval;
155
156  }

157
158  public void Left()
159  {
160    direction = (direction + 1% 4;
161  }

162
163  public void forward(int step)
164  {
165    if (direction == South) //Y++
166    {
167      while (pos.getY() < max && step>0)
168      {
169        if (map[pos.getX()][pos.getY()].getSatus().equals(".")) //第一步也要画
170        {
171          map[pos.getX()][pos.getY()].setStatus("*");
172        }

173        pos.setY(pos.getY() + 1);
174        map[pos.getX()][pos.getY()].setStatus("*");
175        map[pos.getX()][pos.getY()].showPos();
176        step--;
177      }

178    }

179    else if (direction == East) //X++
180    {
181      while (pos.getX() < max && step>0)
182      {
183        if (map[pos.getX()][pos.getY()].getSatus().equals(".")) //第一步也要画
184        {
185          map[pos.getX()][pos.getY()].setStatus("*");
186        }

187        pos.setX(pos.getX() + 1);
188        map[pos.getX()][pos.getY()].setStatus("*");
189        map[pos.getX()][pos.getY()].showPos();
190        step--;
191      }

192
193    }

194    else if (direction == North) //Y--
195    {
196      while (pos.getY() > min && step>0)
197      {
198        if (map[pos.getX()][pos.getY()].getSatus().equals(".")) //第一步也要画
199        {
200          map[pos.getX()][pos.getY()].setStatus("*");
201        }

202        pos.setY(pos.getY() - 1);
203        map[pos.getX()][pos.getY()].setStatus("*");
204        map[pos.getX()][pos.getY()].showPos();
205        step--;
206      }

207    }

208    else if (direction == West ) //X--
209    {
210      while (pos.getX() > min && step>0)
211      {
212        if (map[pos.getX()][pos.getY()].getSatus().equals(".")) //draw the first step
213        {
214          map[pos.getX()][pos.getY()].setStatus("*");
215        }

216        pos.setX(pos.getX() - 1);
217        map[pos.getX()][pos.getY()].setStatus("*");
218        map[pos.getX()][pos.getY()].showPos();
219        step--;
220      }

221    }

222  }

223
224  public static void main(String[] args)
225  {
226    String[] cmds = "FORWARD 19","LEFT","FORWARD 19""LEFT","FORWARD 19","LEFT","FORWARD 17","LEFT","FORWARD 17","LEFT","FORWARD 17","LEFT","FORWARD 13","LEFT","FORWARD 13","LEFT","FORWARD 13","LEFT","FORWARD 13","LEFT","FORWARD 13","LEFT",};
227
228    DrawLines dl = new DrawLines();
229
230    dl.execute(cmds);
231
232    dl.showMap();
233
234  }

235
236}

posted on 2006-02-13 21:36 Vincent.Chen 阅读(546) 评论(0)  编辑  收藏 所属分类: 杂文

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