我的程序沒有分析正確

Question

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import java.util.ArrayList; 
import java.util.Arrays; 

public class Cloud { 
    private ArrayList<Point> points; 
    private double left; 
    private double right; 
    private double top; 
    private double bottom; 

    private final double epsilon = 10e-6; 
    /** 
    * 
    * @param p a Point 
    * @return whether p in the cloud 
    */ 
    public boolean hasPoint(Point p) { 
     return points.contains(p); 
    } 

    /** 
    * Constructor 
    * @param maxSize: points array size 
    */ 
    public Cloud(){ 
     points = new ArrayList<Point>(); 
     this.left = 0.0; 
     this.right = 0.0; 
     this.top = 0.0; 
     this.bottom = 0.0; 
    } 

    /** 
    * 
    * @param p 
    * if (size < maxSize) add p to points, increment size 
    * @return the boolean value returned by the ArrayList add method 
    *   
    */ 
    public boolean addPoint(Point p){ 
     extremes(); 
     return points.add(p); 
    } 

    /** 
    * Use the method toString of ArrayList 
    */ 
    public String toString(){ 
     return points.toString(); 
     } 

    /* 
    * return an array of the double extremes instance variables: 
    *  left, right, top, bottom 
    */ 
    public double[] getExtremes(){ 
     double[] ext = new double[4]; 
     ext[0] = left; 
     ext[1] = right; 
     ext[2] = top; 
     ext[3] = bottom; 

     return ext; 
    } 


    /** 
    * Compute four double values: 
    * left: the x coordinate of a left-most Point 
    * right: the x coordinate of a right-most Point 
    * top: the y coordinate of a highest Point 
    * bottom: the y coordinate of a lowest Point 
    * 
    * and put them in the appropriate instance variables 
    */ 
    private void extremes(){ 
     for (int i=0; i<points.size(); i++){ 
      Point p = points.get(i); 
      if(p.getX() < left){ 
       left = p.getX(); 
      } 
      if(p.getX() > right){ 
       right = p.getX(); 
      } 
      if(p.getY() < bottom){ 
       bottom = p.getY(); 
      } 
      if(p.getY() > top){ 
       top = p.getY(); 
      } 
     } 
    } 

    /** 
    * 
    * @param p1 
    * @param p2 
    * 
    * all Points outside the rectangle, line or point spanned 
    * by p1 and p2 are removed 
    * 
    * After removal, the extreme values left, right, top and bottom 
    * are updated using the extremes method; then using an assert the 
    * extremes of the Cloud are checked using the extremes of the two 
    * Points p1, and p2 
    * 
    */ 
    public void crop(Point p1, Point p2){ 
     if(p1 == p2){ 
      Point temp = p1; 
      points.clear(); 
      points.add(temp); 
     } 
     if(p1.getX() == p2.getX()){ 
      double temp = p1.getX(); 
      for(int i=0; i<points.size(); i++){ 
       if(points.get(i).getX() != temp){ 
        points.remove(i); 
       } 
      } 
     } 
     if(p1.getY() == p2.getY()){ 
      double temp = p1.getY(); 
      for(int i=0; i<points.size(); i++){ 
       if(points.get(i).getY() != temp){ 
        points.remove(i); 
       } 
      } 
     } 
     else{ 
      double tempLeft = p1.getX(); 
      double tempRight = p1.getX(); 
      double tempTop = p1.getY(); 
      double tempBottom = p1.getY(); 
      if(p2.getX() < tempLeft){ 
       tempLeft = p2.getX(); 
      } 
      if(p2.getX() > tempRight){ 
       tempRight = p2.getX(); 
      } 
      if(p2.getY() > tempTop){ 
       tempTop = p2.getY(); 
      } 
      if(p2.getY() < tempBottom){ 
       tempBottom = p2.getY(); 
      } 
      for(int i=0; i<points.size(); i++){ 
       if(points.get(i).getX() < tempLeft){ 
        points.remove(i); 
       } 
       if(points.get(i).getX() > tempRight){ 
        points.remove(i); 
       } 
       if(points.get(i).getY() < tempBottom){ 
        points.remove(i); 
       } 
       if(points.get(i).getY() > tempTop){ 
        points.remove(i); 
       } 
      } 
      } 
    } 
    /* 
    * equality check for doubles 
    */ 
    private boolean dblEq(double a, double b){ 
     return Math.abs(a-b) < epsilon; 
    } 


    /** 
    * @param args: not used 
    */ 
    public static void main(String[] args) { 
     // TODO test all cloud methods 
     Cloud set = new Cloud(); 
     System.out.println("initial set: " + set); 
     for(int i=0; i<5; i++) 
      for (int j=0; j<i; j++){ 
       set.addPoint(new Point(i-j*0.5,j)); 
      } 
     System.out.println("set after addPoints: " + set);   
     double[] ext = set.getExtremes(); 
     if(ext != null) { 
     System.out.println("extremes: " + Arrays.toString(ext)); 
     System.out.println("left of set: " + ext[0]); 
     System.out.println("right of set: " + ext[1]); 
     System.out.println("top of set: " + ext[2]); 
     System.out.println("bottom of set: " + ext[3]); 

     set.crop(new Point(3,0), new Point(2,2)); 
     System.out.println("set after crop 1: " + set); 
     assert set.dblEq(set.left,2.0) && set.dblEq(set.right,3.0) && 
       set.dblEq(set.bottom,0.0) && set.dblEq(set.top,2.0); 

     set.crop(new Point(3,2),new Point(2,2)); 
     System.out.println("set after crop 2: " + set); 
     assert set.dblEq(set.left,2.0) && set.dblEq(set.right,3.0) && 
       set.dblEq(set.bottom,2.0) && set.dblEq(set.top,2.0); 
     } 
    } 

} 

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是這裏的正確值是輸出：

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initial set: [] 

set after addPoints: [(1.0,0.0), (2.0,0.0), (1.5,1.0), (3.0,0.0), (2.5,1.0), (2.0,2.0), (4.0,0.0), (3.5,1.0), (3.0,2.0), (2.5,3.0)] 

extremes: [0.0, 4.0, 2.0, 0.0] 

left of set: 0.0 

right of set: 4.0 

top of set: 2.0 

bottom of set: 0.0 

set after crop 1: [(2.0,0.0), (3.0,0.0), (2.5,1.0), (2.0,2.0), (3.5,1.0), (3.0,2.0)] 

set after crop 2: [(3.0,0.0), (2.0,2.0), (3.0,2.0)] 

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正如你所看到的極端不正確（該集合的頂部應該是3.0），以及它不裁剪正確的值ether。我做錯了什麼？

編輯： 好吧，基本上我的程序是假設給「雲」添加「點數」（兩個雙精度值），並設置極值（距離雲底最遠和最遠的距離，這是一個圖），然後通過並裁剪（設置兩個點並去掉所有不在由給定兩點繪製的正方形中的點）。我希望這有幫助。

Answer 1

在你的加點中，你首先計算極值，然後加上這個點，所以你的最後一點不在這個極端。

public boolean addPoint（Point p）{ extremes（）; return points.add（p）; }

b.t.w爲什麼你不檢查增加點的極端而不是在整個集合上運行它。 唯一的變化可能是由於最後一點的增加。 你建立在O雲（N^2），而不是爲O（n）

羅尼