HDU1401（双向BFS）

题意：http://acm.hdu.edu.cn/showproblem.php?pid=1401

给你8*8的棋盘和4个棋子初始位置、最终位置，问你能否在8次操作后达到该状态。

思路：

双向BFS，起点开始正搜4步，终点倒搜4步，map标记。

#define IOS ios_base::sync_with_stdio(0); cin.tie(0);
#include <cstdio>//sprintf islower isupper
#include <cstdlib>//malloc  exit strcat itoa system("cls")
#include <iostream>//pair
#include <fstream>//freopen("C:\Users\13606\Desktop\Input.txt","r",stdin);
#include <bitset>
//#include <map>
#include<unordered_map>
#include <vector>
#include <stack>
#include <set>
#include <string.h>//strstr substr strcat
#include <string>
#include <time.h>// srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;
#include <cmath>
#include <deque>
#include <queue>//priority_queue<int, vector<int>, greater<int> > q;//less
#include <vector>//emplace_back
//#include <math.h>
#include <cassert>
#include <iomanip>
//#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor
#include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)
using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation
//******************
clock_t __START,__END;
double __TOTALTIME;
void _MS(){__START=clock();}
void _ME(){__END=clock();__TOTALTIME=(double)(__END-__START)/CLOCKS_PER_SEC;cout<<"Time: "<<__TOTALTIME<<" s"<<endl;}
//***********************
#define rint register int
#define fo(a,b,c) for(rint a=b;a<=c;++a)
#define fr(a,b,c) for(rint a=b;a>=c;--a)
#define mem(a,b) memset(a,b,sizeof(a))
#define pr printf
#define sc scanf
#define ls rt<<1
#define rs rt<<1|1
typedef pair<int,int> PII;
typedef vector<int> VI;
typedef unsigned long long ull;
typedef long long ll;
typedef double db;
const double E=2.718281828;
const double PI=acos(-1.0);
const ll INF=(1LL<<60);
const int inf=(1<<30);
const double ESP=1e-9;
const int mod=(int)1e9+7;
const int N=(int)1e6+10;

int mp[10][10];
unordered_map<ull,bool>mark;
struct node
{
    ull id;
    int step;
};
ull get()
{
    ull now=0,temp=1;
    int cnt=-1;
    for(int i=1;i<=8;++i)
    {
        for(int j=1;j<=8;++j)
        {
            ++cnt;
            if(mp[i][j])
                now|=temp<<cnt;
        }
    }
    return now;
}
bool ok(int x,int y)
{
    return x>=1&&x<=8&&y>=1&&y<=8;
}
bool ans;
void bfs(ull start,bool f)
{
    queue<node>q;
    q.push({start,0});
    while(!q.empty())
    {
        node now=q.front();q.pop();
        if(!f)
        {
            if(mark[now.id])continue;
            mark[now.id]=1;
        }
        else
        {
            if(mark[now.id])
            {
                ans=1;
                return;
            }
        }
        if(now.step==4)continue;
        int cnt=-1;
        for(int i=1;i<=8;++i)
        {
            for(int j=1;j<=8;++j)
            {
                ++cnt;
                mp[i][j]=(int)(now.id>>cnt)&1;
            }
        }
        for(int i=1;i<=8;++i)
        {
            for(int j=1;j<=8;++j)
            {
                if(mp[i][j]&&ok(i-1,j)&&mp[i-1][j]==1&&ok(i-2,j)&&mp[i-2][j]==0)
                {
                    mp[i-2][j]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i-2][j]=0,mp[i][j]=1;
                }
                if(mp[i][j]&&ok(i+1,j)&&mp[i+1][j]==1&&ok(i+2,j)&&mp[i+2][j]==0)
                {
                    mp[i+2][j]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i+2][j]=0,mp[i][j]=1;
                }
                if(mp[i][j]&&ok(i,j-1)&&mp[i][j-1]==1&&ok(i,j-2)&&mp[i][j-2]==0)
                {
                    mp[i][j-2]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i][j-2]=0,mp[i][j]=1;
                }
                if(mp[i][j]&&ok(i,j+1)&&mp[i][j+1]==1&&ok(i,j+2)&&mp[i][j+2]==0)
                {
                    mp[i][j+2]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i][j+2]=0,mp[i][j]=1;
                }
                //--------------------------------------------------------------
                if(mp[i][j]==1&&ok(i-1,j)&&mp[i-1][j]==0)
                {
                    mp[i-1][j]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i-1][j]=0;mp[i][j]=1;
                }
                if(mp[i][j]==1&&ok(i+1,j)&&mp[i+1][j]==0)
                {
                    mp[i+1][j]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i+1][j]=0;mp[i][j]=1;
                }
                if(mp[i][j]==1&&ok(i,j-1)&&mp[i][j-1]==0)
                {
                    mp[i][j-1]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i][j-1]=0;mp[i][j]=1;
                }
                if(mp[i][j]==1&&ok(i,j+1)&&mp[i][j+1]==0)
                {
                    mp[i][j+1]=1,mp[i][j]=0;
                    q.push({get(),now.step+1});
                    mp[i][j+1]=0;mp[i][j]=1;
                }
            }
        }
    }
}

int main()
{
    int x,y;
    while(~sc("%d%d",&x,&y))
    {
        ans=0;
        mark.clear();
        mem(mp,0);
        mp[x][y]=1;
        for(int i=2;i<=4;++i)
        {
            sc("%d%d",&x,&y);
            mp[x][y]=1;
        }
        bfs(get(),0);
        mem(mp,0);
        for(int i=1;i<=4;++i)
        {
            sc("%d%d",&x,&y);
            mp[x][y]=1;
        }
        bfs(get(),1);
        if(ans)
            pr("YES
");
        else
            pr("NO
");
    }
    return 0;
}

/**************************************************************************************/