hdu5012 ACM-ICPC 西安赛区E题 Dice

    题目的意思是给定骰子的一个开始状态（六个面的数字），再给定另一个结束状态，问从初始到结束状态最少要走几步，只能前后左右翻滚。

    一开始做题想简单了，以为模拟所有方案就可以了，后来发现模拟的越多越乱，结果没A出来。

    比赛结束后尝试BFS+Hash(记忆化搜索)，先确定四种操作各改变的数组元素，然后搜索，便可以A了。

    代码不够优美，毕竟菜鸟：#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
#include <map>
#include <queue>
#include <ctime>
using namespace std;

#define LL long long
#define ULL unsigned long long
//#define mod 1000000007
#define eps 1e-8
#define MP make_pair
#define RE freopen("in.txt","r",stdin)
#define WE freopen("out.txt","w",stdout)

const int maxn=10000;
string a,b;
char tmp[100],tmp2[100];
int hash[maxn];

string L(string c)
{
char t = c[2];
c[2] = c[0];
c[0] = c[3];
c[3] = c[1];
c[1] = t;
return c;
}

string R(string c)
{
char t = c[1];
c[1] = c[3];
c[3] = c[0];
c[0] = c[2];
c[2] = t;
return c;
}

string F(string c)
{
char t = c[0];
c[0] = c[5];
c[5] = c[1];
c[1] = c[4];
c[4] = t;
return c;
}

string B(string c)
{
char t = c[4];
c[4] = c[1];
c[1] = c[5];
c[5] = c[0];
c[0] = t;
return c;
}

struct node{
string s;
int step;
void print()
{
cout<<s<<endl;
}

unsigned int APHash()
{
unsigned int key = 0;
int i;

for (i=0; i<s.length(); i++)
{
if ((i & 1) == 0)
key ^= ((key << 7) ^ (s[i]) ^ (key >> 3));
else
key ^= (~((key << 11) ^ (s[i]) ^ (key >> 5)));
}
return (key & 0x7FFFFFFF)%maxn;
}
};

void rotate(int i,node &p,node q)
{
if(i==1) p.s = L(q.s);
if(i==2) p.s = R(q.s);
if(i==3) p.s = F(q.s);
if(i==4) p.s = B(q.s);
}

node p;

void print()
{
cout<<a<<endl;
cout<<b<<endl;
cout<<endl;
}

int bfs() {
memset(hash,0,sizeof(hash));
int j,key;
queue<node> q;
q.push(p);
while(!q.empty()) {
node p = q.front();

if(p.s == b)
{
return p.step;
}

node l,r,f,b;
int ll,rr,ff,bb;
rotate(1,l,p);ll=l.APHash();
rotate(2,r,p);rr=r.APHash();
rotate(3,f,p);ff=f.APHash();
rotate(4,b,p);bb=b.APHash();

if(!hash[ll]){
l.step=p.step+1;
hash[ll] = 1;
q.push(l);
}
if(!hash[rr]){
r.step=p.step+1;
hash[rr] = 1;
q.push(r);
}
if(!hash[ff]){
f.step=p.step+1;
hash[ff] = 1;
q.push(f);
}
if(!hash[bb]){
b.step=p.step+1;
hash[bb] = 1;
q.push(b);
}
// cout<<"bfs: "<<p.s<<" hashKey:"<<p.APHash()<<" depth:"<<p.step<<endl;
q.pop();
}
return -1;
}

int main()
{
//RE;
while(gets(tmp)&&gets(tmp2))
{
a="";
b="";
for(int i=0;i<strlen(tmp);i++)
if(tmp[i]!=' ') a+= tmp[i];
for(int i=0;i<strlen(tmp2);i++)
if(tmp2[i]!=' ') b+= tmp2[i];
p.s=a;
p.step=0;
cout<<bfs()<<endl;
}
}