hdu1043 Eight（康拓展开，记录路径）

利用康拓展开可以实现没有重复的hash判重。

用 pre[i] 数组存储上一步 i 。

用 walk[i] 数组存储从 pre[i] 到 i 的方向。

/*
title :Eight
status:AC
by wf,2016.1.10
*/

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <string>
#include <stack>
#include <cmath>
#include <queue>
#include <set>
#include <map>
#define FOR(i,s,t) for(int i = (s) ; i <= (t) ; ++i )

typedef long long ll;
typedef unsigned long long ull;
using namespace std;

const int inf=0x3f3f3f3f;
const int maxn=1e6+5;

int f[9]= {40320,5040,720,120,24,6,2,1,1};

char dir[4][2]= {-1,0,1,0,0,-1,0,1};
char tab[4]= {'d','u','r','l'};

bool vis[maxn];
char next[maxn];

int pre[maxn];
char walk[maxn];

struct node
{
    int x, y,num[3][3];
};

int tmp[9];
int GetHash(int num[3][3])
{
    int index=0;
    for(int i=0;i<3;++i)
    {
        for(int j=0;j<3;++j)
        {
            tmp[index++] = num[i][j];
        }
    }

    int ret=0;
    for(int i=0; i<9; ++i)
    {
        int t=0;
        for(int j=i+1; j<9; ++j)
        {
            if( tmp[j] < tmp[i] )t++;
        }
        ret += f[i]*t;
    }
    return ret;
}

queue<node>q;
void bfs()
{
    node now,next;
    now.x=2;
    now.y=2;
    int index=1;
    for(int i=0; i<3; ++i)
    {
        for(int j=0; j<3; ++j)
        {
            now.num[i][j]=index++;
        }
    }

    //int key = GetHash(now.num);
    //cout<<"debug key=="<<key<<endl;

    while(!q.empty())q.pop();
    q.push(now);

    while(!q.empty())
    {
        now = q.front();
        q.pop();


        int key = GetHash(now.num);
        vis[key]=1;

        for(int i=0; i<4; ++i)
        {

            int nx=now.x+dir[i][0];
            int ny=now.y+dir[i][1];

            if(nx<0 || nx>=3)continue;
            if(ny<0 || ny>=3)continue;

            swap(now.num[now.x][now.y] , now.num[nx][ny]);
            int key2 = GetHash(now.num);
            if( !vis[key2] )
            {
                next.x=nx;
                next.y=ny;
                for(int i=0;i<3;++i)
                {
                    for(int j=0;j<3;++j)
                    {
                        next.num[i][j]=now.num[i][j];
                    }
                }

                pre[key2]=key;
                walk[key2]=tab[i];
                q.push(next);
            }
            swap(now.num[now.x][now.y] , now.num[nx][ny]);
        }
    }


}


int main()
{
    //#ifndef ONLINE_JUDGE
    //freopen("in.txt","r",stdin);
    //#endif

    memset(vis,0,sizeof 0);
    bfs();

    char mp[9];
    while(cin>>mp[0])
    {
        for(int i=1;i<9;++i)
        {
            cin>>mp[i];
        }
        int index=0,num[3][3];
        for(int i=0;i<3;++i)
        {
            for(int j=0;j<3;++j)
            {
                if(mp[index]=='x')mp[index]='9';
                num[i][j] =  mp[index++] - '0';
            }
        }
        int key = GetHash(num);

        if( !vis[key] )
        {
            cout<<"unsolvable"<<endl;
            continue;
        }

        while(key!=0)
        {
            cout<<walk[key];
            key=pre[key];
        }
        cout<<endl;
    }

}