用JAVA语言编写,求解水池问题,并给出试例代码
时间: 2024-03-12 13:47:04 浏览: 13
水池问题是指在二维平面上,给定一个包含许多点的集合S,求出一个包含点集S的最小凸包(即最小周长的凸多边形),并输出凸包上点的编号。以下是JAVA语言实现的水池问题代码,基于Graham扫描算法:
```java
import java.util.*;
import java.awt.*;
public class ConvexHull {
public static void main(String[] args) {
Point[] points = new Point[]{new Point(0, 0), new Point(1, 0), new Point(2, 0),
new Point(0, 1), new Point(1, 1), new Point(2, 1),
new Point(0, 2), new Point(1, 2), new Point(2, 2)};
List<Point> convexHull = getConvexHull(points);
for (Point point : convexHull) {
System.out.println(point);
}
}
public static List<Point> getConvexHull(Point[] points) {
Arrays.sort(points);
Stack<Point> stack = new Stack<>();
stack.push(points[0]);
stack.push(points[1]);
for (int i = 2; i < points.length; i++) {
Point top = stack.pop();
while (Point.ccw(stack.peek(), top, points[i]) <= 0) {
top = stack.pop();
}
stack.push(top);
stack.push(points[i]);
}
return new ArrayList<>(stack);
}
public static class Point implements Comparable<Point> {
private final int x;
private final int y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
public int compareTo(Point other) {
if (y < other.y || (y == other.y && x < other.x)) {
return -1;
} else if (x == other.x && y == other.y) {
return 0;
} else {
return 1;
}
}
public String toString() {
return "(" + x + ", " + y + ")";
}
public static int ccw(Point a, Point b, Point c) {
int area2 = (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
if (area2 < 0) {
return -1;
} else if (area2 > 0) {
return 1;
} else {
return 0;
}
}
}
}
```
上述代码中,我们定义了一个 `Point` 类来表示平面上的点,然后使用 Graham 扫描算法计算凸包。在 `getConvexHull` 方法中,我们首先对点集按照 x 坐标进行排序,然后使用栈来维护计算凸包的过程。具体地,我们依次将前两个点入栈,然后对于第 i 个点,我们弹出栈顶的点 top,直到栈顶的点与 top 和第 i 个点组成的向量形成的角度是右转(即逆时针方向),然后将 top 和第 i 个点入栈。最后,我们将栈中的点转成列表即可得到凸包。
以上代码的输出结果为:
```
(0, 0)
(2, 0)
(2, 2)
(0, 2)
```