八皇后问题（递归版）

/**
 * @author phinecos
 * @since 2008/10/31
 */
class EightQueen
{ 
    static final int MAXSIZE = 8;//棋盘大小
    static int okTimes = 0; //解法个数
    static int[][] chess = new int[MAXSIZE][MAXSIZE];//棋盘

    public static boolean CanPut(int row,int col)
    {//皇后能否放置在chess[row][col]的位置上
        //第row行不能有多于1个皇后
        int i,j;
        for(i=0;i<MAXSIZE;++i)
        {
            if(chess[row][i]==1)
                return false;
        }
        //第col列不能有多于1个皇后
        for(i=0;i<MAXSIZE;++i)
        {
            if(chess[i][col]==1)
                return false;
        }
        //对角线不能有多于1个皇后
        //反对角线
        for(i=row-1,j=col+1;i>=0&&j<MAXSIZE;--i,++j)
        { 
            if(chess[i][j]==1)
                return false;
        }
        for(i=row+1,j=col-1;i<MAXSIZE&&j>=0;++i,--j)
        {
            if(chess[i][j]==1)
                return false;
        }    
        //对角线
        for(i=row-1,j=col-1;i>=0&&j>=0;--i,--j)
        {
            if(chess[i][j]==1)
                return false;
        }
        for(i=row+1,j=col+1;i<MAXSIZE&&j<MAXSIZE;++i,++j)
        {
            if(chess[i][j]==1)
                return false;
        }
        return true;
    }
    public static void Solve(int curChess,int num)
    {
        if(num==8)
        {//八个皇后了，
            okTimes++;
            return;
        }
        else
        {
            if(curChess<64)
            {
                int i,j;
                i=curChess/MAXSIZE;//行
                j=curChess%MAXSIZE;//列
                if(chess[i][j]==0&&CanPut(i,j)==true)
                {//chesss[i][j]空着，并且经测试可以放置
                    chess[i][j]=1; //放置皇后下去
                    Solve(curChess+1,num+1);
                    chess[i][j]=0; //回溯
                }
                Solve(curChess+1,num); //chess[i][j]无法放置，跳过它
            }
        }
    }
    public static void main(String args[])
    { 
        int i,j;
        for(i=0;i<MAXSIZE;++i)
            for(j=0;j<MAXSIZE;++j)
            {
                chess[i][j] = 0;
            }
        Solve(0,0);
        System.out.println("八皇后问题共有"+okTimes+"个解法"); 
    }
}