AStar 算法简述(unity c#代码段)

[zhhf96]

A*（A-Star)算法是一种静态路网中求解最短路最有效的直接搜索方法。
注意是最有效的直接搜索算法。之后涌现了很多预处理算法（ALT，CH，HL等等），在线查询效率是A*算法的数千甚至上万倍。
公式表示为： f(n)=g(n)+h(n)
其中 f(n) 是从初始点经由节点n到目标点的估价函数，
g(n) 是在状态空间中从初始节点到n节点的实际代价，
h(n) 是从n到目标节点最佳路径的估计代价。
保证找到最短路径（最优解的）条件，关键在于估价函数f(n)的选取：
估价值h(n)<= n到目标节点的距离实际值，这种情况下，搜索的点数多，搜索范围大，效率低。但能得到最优解。并且如果h(n)=d(n)，即距离估计h(n)等于最短距离，那么搜索将严格沿着最短路径进行， 此时的搜索效率是最高的。
如果 估价值>实际值,搜索的点数少，搜索范围小，效率高，但不能保证得到最优解。

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public enum GridType
{
	Normal,//正常
	Obstacle,//障碍物
	Start,//起点
	End//终点
}

//为了格子排序 需要继承IComparable接口实现排序
public class MapGrid : IComparable//排序接口
{
	public int x;//记录坐标
	public int y;

	public int f;//总消耗
	public int g;//当前点到起点的消耗
	public int h;//当前点到终点的消耗


	public GridType type;//格子类型
	public MapGrid fatherNode;//父节点


	//排序
	public int CompareTo(object obj)	 //排序比较方法 ICloneable的方法
	{
		//升序排序
		MapGrid grid = (MapGrid)obj;
		if (this.f < grid.f)
		{
			return -1;					//升序
		}
		if (this.f > grid.f)
		{
			return 1;					//降序
		}
		return 0;
	}

}




public class AStar : MonoBehaviour
{
	//格子大小
	public int row = 5;
	public int col = 10;
	public int size = 70;				//格子大小

	public MapGrid[,] grids;			//格子数组

	public ArrayList openList;			//开启列表
	public ArrayList closeList;			//结束列表

	//开始,结束点位置
	private int xStart = 2;
	private int yStart = 1;

	private int xEnd = 2;
	private int yEnd = 5;
	private Stack<string> fatherNodeLocation;

	void Init()
	{
		grids = new MapGrid[row, col];	//初始化数组
		for (int i = 0; i < row; i++)
		{
			for (int j = 0; j < col; j++)
			{
				grids[i, j] = new MapGrid();
				grids[i, j].x = i;
				grids[i, j].y = j;		//初始化格子,记录格子坐标
			}
		}
		grids[xStart, yStart].type = GridType.Start;
		grids[xStart, yStart].h = Manhattan(xStart, yStart);	//起点的 h 值

		grids[xEnd, yEnd].type = GridType.End;					//结束点
		fatherNodeLocation = new Stack<string>();

		//生成障碍物
		for (int i = 1; i <= 3; i++)
		{
			grids[i, 3].type = GridType.Obstacle;
		}

		openList = new ArrayList();
		openList.Add(grids[xStart, yStart]);
		closeList = new ArrayList();
	}

	int Manhattan(int x, int y)					//计算算法中的 h
	{
		return (int)(Mathf.Abs(xEnd - x) + Mathf.Abs(yEnd - y)) * 10;
	}


	// Use this for initialization
	void Start()
	{
		Init();
	}

	void DrawGrid()
	{
		for (int i = 0; i < row; i++)
		{
			for (int j = 0; j < col; j++)
			{
				Color color = Color.yellow;
				if (grids[i, j].type == GridType.Start)
				{
					color = Color.green;
				}
				else if (grids[i, j].type == GridType.End)
				{
					color = Color.red;
				}
				else if (grids[i, j].type == GridType.Obstacle)	//障碍颜色
				{
					color = Color.blue;
				}
				else if (closeList.Contains(grids[i, j]))		//关闭列表颜色  如果当前点包含在closList里
				{
					color = Color.yellow;
				}
				else { color = Color.gray; }

				GUI.backgroundColor = color;
				GUI.Button(new Rect(j * size, i * size, size, size), FGH(grids[i, j]));
			}
		}
	}

	//每个格子显示的内容
	string FGH(MapGrid grid)
	{
		string str = "F" + grid.f + "\n";
		str += "G" + grid.g + "\n";
		str += "H" + grid.h + "\n";
		str += "(" + grid.x + "," + grid.y + ")";
		return str;
	}
	void OnGUI()
	{
		DrawGrid();
		for (int i = 0; i < openList.Count; i++)
		{
			//生成一个空行,存放开启数组
			GUI.Button(new Rect(i * size, (row + 1) * size, size, size), FGH((MapGrid)openList[i]));
		}
			//生成一个空行,存放关闭数组
		for (int j = 0; j < closeList.Count; j++)
		{
			GUI.Button(new Rect(j * size, (row + 2) * size, size, size), FGH((MapGrid)closeList[j]));
		}

		if (GUI.Button(new Rect(col * size, size, size, size), "next"))
		{
			NextStep();//点击到下一步
		}
	}

	void NextStep()
	{
		if (openList.Count == 0)				//没有可走的点
		{
			print("Over !");
			return;
		}
		MapGrid grid = (MapGrid)openList[0];	//取出openList数组中的第一个点
		if (grid.type == GridType.End)			//找到终点
		{
			print("Find");
			ShowFatherNode(grid);		//找节点//打印路线
			return;
		}

		for (int i = -1; i <= 1; i++)
		{
			for (int j = -1; j <= 1; j++)
			{
				if (!(i == 0 && j == 0))
				{
					int x = grid.x + i;
					int y = grid.y + j;
					//x,y不超过边界,不是障碍物,不在closList里面
					if (x >= 0 && x < row && y >= 0 && y < col && grids[x, y].type != GridType.Obstacle && !closeList.Contains(grids[x, y]))
					{


						//到起点的消耗
						int g = grid.g + (int)(Mathf.Sqrt((Mathf.Abs(i) + Mathf.Abs(j))) * 10);
						if (grids[x, y].g == 0 || grids[x, y].g > g)
						{
							grids[x, y].g = g;
							grids[x, y].fatherNode = grid;		//更新父节点
						}
						//到终点的消耗
						grids[x, y].h = Manhattan(x, y);		
						grids[x, y].f = grids[x, y].g + grids[x, y].h;
						if (!openList.Contains(grids[x,y]))
						{
							openList.Add(grids[x, y]);			//如果没有则加入到openlist
						}
						openList.Sort();						//排序
					}
				}
			}
		}
		//添加到关闭数组
		closeList.Add(grid);
		//从open数组删除
		openList.Remove(grid);
	}


	//回溯法 递归父节点
	void ShowFatherNode(MapGrid grid)
	{
		if (grid.fatherNode != null)
		{
			//print(grid.fatherNode.x + "," + grid.fatherNode.y);
			string str = grid.fatherNode.x + "," + grid.fatherNode.y;
			fatherNodeLocation.Push(str);
			ShowFatherNode(grid.fatherNode);
		}
		if (fatherNodeLocation.Count!=0)
		{
			print(fatherNodeLocation.Pop());
		}
	}

	
}

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[wolf96]

好物

[carawola]

就看看～～～～～～～·

[kujibiu]

有点复杂@@@@@@@@@@@2