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| import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* The Class Main.
*
* Created on: 13.08.2011
*
* @author: M128K145
*/
public class Main {
/**
* The Class PairDouble.
*
* Created on: 13.08.2011
*
* @author: M128K145
*/
public static class PairDouble implements Comparator<PairDouble> {
/** The first. */
private double first;
/** The second. */
private double second;
/**
* Instantiates a new pair double.
*/
public PairDouble() {
this.setFirst(0);
this.setSecond(0);
}
/**
* Instantiates a new pair double.
*
* @param first
* the first
* @param second
* the second
*/
public PairDouble(double first, double second) {
this.setFirst(first);
this.setSecond(second);
}
/**
* Gets the first.
*
* @return the first
*/
public double getFirst() {
return first;
}
/**
* Sets the first.
*
* @param first
* the first to set
*/
public void setFirst(double first) {
this.first = first;
}
/**
* Gets the second.
*
* @return the second
*/
public double getSecond() {
return second;
}
/**
* Sets the second.
*
* @param second
* the second to set
*/
public void setSecond(double second) {
this.second = second;
}
/**
* Compare.
*
* @param o1
* the o1
* @param o2
* the o2
* @return the int
* @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
*/
@Override
public int compare(PairDouble o1, PairDouble o2) {
double tmp = o1.getFirst() - o2.getSecond();
return tmp < 0 ? -1 : tmp == 0 ? 0 : 1;
}
}
/**
* The Class PairDoubleComparator.
*
* Created on: 13.08.2011
*
* @author: M128K145
*/
public static class PairDoubleComparator implements Comparator<PairDouble> {
/**
* Compare.
*
* @param o1
* the o1
* @param o2
* the o2
* @return the int
* @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
*/
public int compare(PairDouble o1, PairDouble o2) {
double tmp = o1.getFirst() - o2.getFirst();
return tmp < 0 ? -1 : tmp == 0 ? 0 : 1;
}
}
/**
* Cw.
*
* @param a
* the a
* @param b
* the b
* @param c
* the c
* @return true, if successful
*/
private static boolean cw(final PairDouble a, final PairDouble b,
final PairDouble c) {
return (b.getFirst() - a.getSecond()) * (c.second - a.second)
- (b.second - a.second) * (c.first - a.first) < 0;
}
/**
* Convex hull.
*
* @param p
* the p
* @return the list
*/
private static List<PairDouble> convexHull(List<PairDouble> p) {
int n = p.size();
if (n <= 1)
return p;
int k = 0;
Collections.sort(p, new PairDoubleComparator());
List<PairDouble> q = new ArrayList<PairDouble>();
for (int i = 0; i < n; q.add(p.get(i++)), ++k)
for (; k >= 2 && !cw(q.get(k - 2), q.get(k - 1), p.get(i)); --k)
;
for (int i = n - 2, t = k; i >= 0; q.add(p.get(i--)), ++k)
for (; k > t && !cw(q.get(k - 2), q.get(k - 1), p.get(i)); --k)
;
resize(q, k - 1 - (q.get(0) == q.get(1) ? 1 : 0));
return q;
}
/**
* Resize.
*
* @param <T>
* the generic type
* @param list
* the list
* @param size
* the size
* @return the list
*/
private static <T> List<T> resize(List<T> list, int size) {
if (list.size() > size) {
for (int i = list.size() - 1; i >= size - 1; list.remove(i), --i)
;
} else if (list.size() < size) {
T temp = list.get(list.size() - 1);
for (int i = 0, iSize = size - list.size(); i < iSize; list.add(temp), ++i)
;
}
return list;
}
/**
* The main method.
*
* @param args
* the arguments
*/
public static void main(String[] args) {
List<PairDouble> points = new ArrayList<PairDouble>();
points.add(0, new PairDouble(0, 0));
points.add(1, new PairDouble(3, 0));
points.add(2, new PairDouble(0, 3));
points.add(3, new PairDouble(1, 1));
List<PairDouble> hull = convexHull(points);
System.out.println(3 == hull.size());
}
} |
(
