A*算法【拼图游戏】

数据结构

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace 拼图
{
 
    /// <summary>
    /// 空格移动的方向
    /// </summary>
    enum Direction
    {
        None,
        Up,
        Left,
        Right,
        Down
    }
 
    /// <summary>
    /// 解答
    /// </summary>
    enum Answer
    {
        /// <summary>
        /// 不存在解答
        /// </summary>
        NotExist,
        /// <summary>
        /// 存在解答
        /// </summary>
        Exist,
        /// <summary>
        /// 在当前指定的搜索深度内不存在解答（需要扩大深度）
        /// </summary>
        NotExistInDepth
    }
 
    /// <summary>
    /// 局面状态信息
    /// </summary>
    class StateMsg
    {
        private int depth;
        private Direction dir;
        public int Depth
        {
            get { return depth; }
        }
        public Direction Dir
        {
            get { return dir; }
        }
 
        public StateMsg(int depth, Direction dir)
        {
            this.depth = depth;
            this.dir = dir;
        }
    }
 
    /// <summary>
    /// 局面状态
    /// </summary>
    class State : StateMsg
    {
        private long code;
 
        /// <summary>
        /// 棋盘的编码
        /// </summary>
        public long Code
        {
            get { return code; }
            set { code = value; }
        }
 
        public State(long code, int depth, Direction dir)
            : base(depth, dir)
        {
            this.code = code;
        }
    }
}

Astar类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace 拼图
{
    class AStar
    {
 
        /// <summary>
        /// ten[i]代表10的i次方
        /// </summary>
        private static readonly long[] tens = { , , , , , , , , ,  };
 
        /// <summary>
        /// 不是合理的编码
        /// </summary>
        private const int OutOfCode = -;
 
        /// <summary>
        /// 标志是否找到目标状态的编码
        /// </summary>
        public const int WinnerCode = ;
 
        private Direction[][] dirs;
 
        private int startBoard;
        private static int endBoard;
        private static int[] endBoardArray;
 
        private int MaxDepth;
 
        private SortedList<long, StateMsg> openList;
        private Dictionary<long, StateMsg> boardtable;
 
        private const  long  maxNodes = ; //至多搜索的结点数＝最大局面状态数量：（9!）=362880；
 
        private long nodes;
        private int same;
        private float time;
        private Direction[] result;
 
        /// <summary>
        /// 已经访问的结点数量
        /// </summary>
        public long Nodes
        {
            get { return nodes; }
        }
 
        /// <summary>
        /// 重复访问相同结点的数量
        /// </summary>
        public int Same
        {
            get { return same; }
        }
 
        public float Time
        {
            get { return time; }
        }
 
        public static int N;
 
        /// <summary>
        /// 最终结果
        /// </summary>
        public Direction[] Result
        {
            get { return result; }
        }
 
        public AStar(int n)
        {
            N = n;
            dirs = new Direction[n*n][];
            if(n==)
            {
                dirs[] = new Direction[] { Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Left, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Right };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Up };
                dirs[] = new Direction[] { Direction.Up, Direction.Left };
            }
            else
            {
                dirs[] = new Direction[] { Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Left, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Right, Direction.Down };
 
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
 
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Right, Direction.Down };
 
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
 
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Right, Direction.Down };
 
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Right, Direction.Down };
 
                dirs[] = new Direction[] { Direction.Up, Direction.Left, Direction.Down };
                dirs[] = new Direction[] { Direction.Up, Direction.Right };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Up };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Up };
                dirs[] = new Direction[] { Direction.Left, Direction.Right, Direction.Up };
                dirs[] = new Direction[] { Direction.Up, Direction.Left };
            }
 
        }
 
        /// <summary>
        /// 求与目标位置不同的个数（不计空格，因此返回值0～8）
        /// </summary>
        /// <param name="curboard"></param>
        /// <returns></returns>
        public static int Different(int curboard)
        {
            int t_start = curboard;
            int emp_start = curboard % ;
            int ev = ;
            //写2个for是为了减少9个if
            for (int i = N*N; i > emp_start; i--)
            {
                t_start /= ;
                if (t_start %  != endBoardArray[i])
                    ev++;
            }
            for (int i = emp_start - ; i >= ; i--)
            {
                t_start /= ;
                if (t_start %  != endBoardArray[i])
                    ev++;
            }
            return ev;
        }
 
        public static int getBoard(long code)
        {
            return (int)(code % tens[]);
        }
 
        private static int getEval(long code)
        {
            return (int)(code / tens[]);
        }
 
        private static int getEmpIndex(long code)
        {
            return (int)(code % );
        }
 
        private static long combinCode(int board, int eval)
        {
            long codehead = eval * tens[];
            return codehead + board;
        }
 
        /// <summary>
        /// 改变局面(移动空格)
        /// </summary>
        /// <param name="code"></param>
        /// <param name="dir"></param>
        public static long change(long code, Direction dir)
        {
            int newboard;
            int eval;
            int num;
            int t0;
            long t1;
            long t2;
            switch (dir)
            {
                case Direction.Left:
                    newboard = getBoard(code) - ;
                    if (newboard == endBoard)
                        return WinnerCode;
                    eval = Different(newboard);
                    return combinCode(newboard, eval);
                case Direction.Right:
                    newboard = getBoard(code) + ;
                    if (newboard == endBoard)
                        return WinnerCode;
                    eval = Different(newboard);
                    return combinCode(newboard, eval);
                case Direction.Up:
                    num = getBoard(code);
                    t0 = N*N - num %  + ;
                    t1 = num / tens[t0];
                    t2 = t1 % ;
                    t1 = t1 - t2 + (t2 % ) *  + t2 / ;
                    t1 *= tens[t0];
                    newboard = (int)(t1 + ((num % tens[t0]) - N));
                    if (newboard == endBoard)
                        return WinnerCode;
                    eval = Different(newboard);
                    return combinCode(newboard, eval);
                case Direction.Down:
                    num = getBoard(code);
                    t0 = N*N - num %  +  - N;//跟Up不同的地方
                    t1 = num / tens[t0];
                    t2 = t1 % ;
                    t1 = t1 - t2 + (t2 % ) *  + t2 / ;//跟Up不同的地方
                    t1 *= tens[t0];
                    newboard = (int)(t1 + ((num % tens[t0]) + N));//跟Up不同的地方
                    if (newboard == endBoard)
                        return WinnerCode;
                    eval = Different(newboard);
                    return combinCode(newboard, eval);
            }
            return OutOfCode;
        }
 
        /// <summary>
        /// 恢复上一步的局面
        /// </summary>
        /// <param name="code"></param>
        /// <param name="dir"></param>
        public long unchange(long code, Direction dir)
        {
            return change(code, (Direction)( - dir));
        }
 
        /// <summary>
        /// 当找到目标时，从哈希表里找原来的路径
        /// </summary>
        /// <param name="endCode"></param>
        /// <param name="depth"></param>
        private void setResult(long endCode, Direction curDir, Direction lastDir, int depth)
        {
            long lastCode = endCode;
            result = new Direction[depth];
            result[depth - ] = curDir;
            for (int i = depth - ; i >= ; i--)
            {
                if (boardtable.ContainsKey(lastCode))
                {
                    result[i] = boardtable[lastCode].Dir;
                    lastCode = unchange(lastCode, result[i]);
                }
                else
                    return;
            }
        }
 
        //本算法的核心部分
        #region 带Open表和HashTable的最好优先搜索(每次扩展Open表后都对Open表排序）
 
        /// <summary>
        ///  扩展Open表
        /// </summary>
        /// <param name="board"></param>
        /// <param name="depth"></param>
        private bool extentOpenList(long code, Direction lastDir, int depth)
        {
            int empIndex = (int)(code %  - );
            int len_moves = dirs[empIndex].Length;
            long newcode;
            Direction dir =  - lastDir;
            for (int i = ; i < len_moves; i++)
                if (dirs[empIndex][i] != dir)
                {
                    newcode = change(code, dirs[empIndex][i]);
 
                    //跟目标匹配,结束
                    if (newcode == WinnerCode)
                    {
                        setResult(code, dirs[empIndex][i], lastDir, depth);
                        return true;
                    }
                    if (newcode <= tens[])
                        throw new Exception("棋盘码修改错误！ ");
                    if (newcode != OutOfCode)
                    {
                        if (!openList.ContainsKey(newcode))
                        {
                            if (!boardtable.ContainsKey(newcode))
                                openList.Add(newcode, new StateMsg(depth, dirs[empIndex][i]));
                            else
                            {
                                same++;
                                if (depth < boardtable[newcode].Depth)
                                {
                                    boardtable.Remove(newcode);
                                    openList.Add(newcode, new StateMsg(depth, dirs[empIndex][i]));
                                }
                            }
                        }
                        else
                        {
                            same++;
                            if (depth < openList[newcode].Depth)
                                openList[newcode] = new StateMsg(depth, dirs[empIndex][i]);
                        }
                    }
                }
            return false;
        }
 
        /// <summary>
        /// 带Open表和HashTable的最好优先搜索(每次扩展Open表后都对Open表排序）
        /// </summary>
        /// <returns></returns>
        private int BestFirstSearch()
        {
            int depth = ;
            Direction[] moves;
            int board;
            long newCode = combinCode(this.startBoard, );
            int empIndex = getEmpIndex(newCode);
 
            moves = dirs[empIndex - ];
            StateMsg data;
            if (extentOpenList(newCode, Direction.None, depth))
                return WinnerCode;
            while (openList.Count > )
            {
                lock (this)
                {
                    nodes++;
                    if (nodes >= maxNodes)
                        return -;
                    newCode = openList.Keys[];
                    board = getBoard(newCode);
                    data = openList[newCode];
                    if (data.Depth != )
                    {
                        depth = data.Depth;
                        if (board == endBoard)
                        {
                            return WinnerCode;
                        }
                        boardtable.Add(newCode, new StateMsg(depth, data.Dir));
                        openList.RemoveAt();
                        if (depth < MaxDepth)
                            if (extentOpenList(newCode, data.Dir, depth + ))
                                return WinnerCode;
                    }
                }
            }
            return -;
        }
 
        #endregion
 
        /// <summary>
        /// 把一维数组的局面编码成一个整数的表示形式
        /// </summary>
        /// <param name="genBoard"></param>
        /// <returns></returns>
        public int ToIntBoard(int[] genBoard)
        {
            int board = ;
            int emp = ;
            for (int i = ; i < genBoard.Length; i++)
            {
                if (genBoard[i] != )
                    board =  * board + genBoard[i];
                else
                    emp = i + ;
            }
            return  * board + emp;
        }
 
        /// <summary>
        /// 判断是否可以从初始状态到达目标状态（计算两个状态的逆序列，奇偶性相同的返回true）
        /// </summary>
        /// <param name="start"></param>
        /// <param name="end"></param>
        /// <returns></returns>
        private bool ExistAns(int[] start, int[] end)
        {
            int sequence_start = , sequence_end = ;
            for (int i = ; i < start.Length; i++)
            {
                if (start[i] != )
                    for (int j = i + ; j < start.Length; j++)
                    {
                        if (start[j] !=  && start[j] < start[i])
                            sequence_start++;
                    }
                if (end[i] != )
                    for (int j = i + ; j < start.Length; j++)
                    {
                        if (end[j] !=  && end[j] < end[i])
                            sequence_end++;
                    }
            }
            return (sequence_start + sequence_end) %  == ;
        }
 
        /// <summary>
        /// 初始化求解
        /// </summary>
        /// <param name="start"></param>
        /// <param name="end"></param>
        /// <param name="maxDepth"></param>
        private void InitComp(int[] start, int[] end, int maxDepth)
        {
            nodes = ;
            same = ;
            MaxDepth = maxDepth;
            result = null;
            boardtable = new Dictionary<long, StateMsg>();
            openList = new SortedList<long, StateMsg>();
            //openStack = new Stack<State>();
            //openQueue = new Queue<State>();
 
            this.startBoard = ToIntBoard(start);
            endBoard = ToIntBoard(end);
            int t_end = endBoard;
            int emp_end = endBoard % ;
            endBoardArray = new int[N*N+];
            endBoardArray[] = emp_end;
            endBoardArray[emp_end] = ;
            for (int i = N*N; i > emp_end; i--)
            {
                t_end /= ;
                endBoardArray[i] = t_end % ;
            }
            for (int i = emp_end - ; i >= ; i--)
            {
                t_end /= ;
                endBoardArray[i] = t_end % ;
            }
        }
 
        /// <summary>
        /// 求解8数码问题
        /// </summary>
        /// <param name="start"></param>
        /// <param name="end"></param>
        /// <param name="maxDepth"></param>
        /// <returns></returns>
        public Answer Compute(int[] start, int[] end, int maxDepth)
        {
            if (!ExistAns(start, end))
                return Answer.NotExist;
            InitComp(start, end, maxDepth);
            if (startBoard == endBoard)
                return Answer.Exist;
            long oldtime = System.DateTime.Now.Ticks;
            int eval = ;
            eval = BestFirstSearch();
            time = (System.DateTime.Now.Ticks - oldtime) / 10000000.0f;
            if (eval == WinnerCode)
                return Answer.Exist;
            return Answer.NotExistInDepth;
        }
 
    }
}