AStar算法的学习
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摘自:http://www.cnblogs.com/hxsyl/p/3994730.html
A*算法的java实现
import java.util.ArrayList; import java.util.Collections; import java.util.Stack; /** * @author pang * */ public class AStartPathFind { //前四个上下左右 public final static int[] dx = { 0, -1, 0, 1, -1, -1, 1, 1 }; public final static int[] dy = { -1, 0, 1, 0, 1, -1, -1, 1 }; // 最外圈都是1表示不可通过 final static public int[][] map = { { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 } }; public static void main(String[] args) { // TODO Auto-generated method stub Point start = new Point(1, 1); Point end = new Point(10, 13); /* * 第一个问题:起点FGH需要初始化吗? 看参考资料的图片发现不需要 */ Stack<Point> stack = printPath(start, end); if (null == stack) { System.out.println("不可达"); } else { while (!stack.isEmpty()) { // 输出(1,2)这样的形势需要重写toString System.out.print(stack.pop() + " -> "); } System.out.println(); } } public static Stack<Point> printPath(Point start, Point end) { /* * 不用PriorityQueue是因为必须取出存在的元素 */ ArrayList<Point> openTable = new ArrayList<Point>(); ArrayList<Point> closeTable = new ArrayList<Point>(); openTable.clear(); closeTable.clear(); Stack<Point> pathStack = new Stack<Point>(); start.parent = null; // 该点起到转换作用,就是当前扩展点 Point currentPoint = new Point(start.x, start.y); // closeTable.add(currentPoint); boolean flag = true; while (flag) { for (int i = 0; i < 8; i++) { int fx = currentPoint.x + dx[i]; int fy = currentPoint.y + dy[i]; Point tempPoint = new Point(fx, fy); if (map[fx][fy] == 1) { // 由于边界都是1中间障碍物也是1,,这样不必考虑越界和障碍点扩展问题 // 如果不设置边界那么fx >=map.length &&fy>=map[0].length判断越界问题 continue; } else { if (end.equals(tempPoint)) { flag = false; // 不是tempPoint,他俩都一样了此时 end.parent = currentPoint; break; } if (i < 4) { tempPoint.G = currentPoint.G + 10; } else { tempPoint.G = currentPoint.G + 14; } tempPoint.H = Point.getDis(tempPoint, end); tempPoint.F = tempPoint.G + tempPoint.H; // 因为重写了equals方法,所以这里包含只是按equals相等包含 // 这一点是使用java封装好类的关键 if (openTable.contains(tempPoint)) { int pos = openTable.indexOf(tempPoint); Point temp = openTable.get(pos); if (temp.F > tempPoint.F) { openTable.remove(pos); openTable.add(tempPoint); tempPoint.parent = currentPoint; } } else if (closeTable.contains(tempPoint)) { int pos = closeTable.indexOf(tempPoint); Point temp = closeTable.get(pos); if (temp.F > tempPoint.F) { closeTable.remove(pos); openTable.add(tempPoint); tempPoint.parent = currentPoint; } } else { openTable.add(tempPoint); tempPoint.parent = currentPoint; } } }// end for if (openTable.isEmpty()) { return null; }// 无路径 if (false == flag) { break; }// 找到路径 openTable.remove(currentPoint); closeTable.add(currentPoint); Collections.sort(openTable); currentPoint = openTable.get(0); }// end while Point node = end; while (node.parent != null) { pathStack.push(node); node = node.parent; } return pathStack; } } class Point implements Comparable<Point> { int x; int y; Point parent; int F, G, H; public Point(int x, int y) { super(); this.x = x; this.y = y; this.F = 0; this.G = 0; this.H = 0; } @Override public int compareTo(Point o) { // TODO Auto-generated method stub return this.F - o.F; } @Override public boolean equals(Object obj) { Point point = (Point) obj; if (point.x == this.x && point.y == this.y) return true; return false; } public static int getDis(Point p1, Point p2) { int dis = Math.abs(p1.x - p2.x) * 10 + Math.abs(p1.y - p2.y) * 10; return dis; } @Override public String toString() { return "(" + this.x + "," + this.y + ")"; } }
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