poj 1077 Eight（bfs，dbfs）

  1 #include <iostream>
  2 #include <map>
  3 #include <algorithm>
  4 #include <string>
  5 #include <queue>
  6 using namespace std;
  7 typedef long long LL;
  8 
  9 int eight[3][3], xx, xy, dx[]={0,0,-1,1,0}, dy[]={0,1,0,0,-1};
 10 char dir[] = "orudl";
 11 
 12 LL encode(){
 13     LL s=eight[2][2];
 14     for(int i=7; i>=0; --i){
 15         s <<=4;
 16         s |= eight[i/3][i%3];
 17     }
 18     return s;
 19 }
 20 void decode(LL s){
 21     for(int i=0; i<9; ++i){
 22         eight[i/3][i%3] = s%16;
 23         if(s%16 == 0) 
 24             xx = i/3, xy = i%3;
 25         s >>=4;
 26     }
 27 }
 28 void print_state(LL s){
 29     printf("s:%d,xx,xy:", s);
 30     decode(s);
 31     printf("%d,%d\n",xx,xy);
 32     for(int i=0; i<3; ++i){
 33         for(int j=0; j<3; ++j)
 34             printf("%d ", eight[i][j]);
 35         printf("\n");
 36     }
 37 
 38 }
 39 queue<LL> que[2];
 40 map<LL,pair<int,LL> > mp[2];// pair:d,ps
 41 
 42 void print(LL s){
 43     int d = mp[0][s].first;
 44     LL ts=s;
 45     string ope;
 46     while(d!=-1){
 47         ope.push_back(dir[d]);
 48         ts = mp[0][ts].second;
 49         d = mp[0][ts].first;
 50     }
 51     reverse(ope.begin(), ope.end());
 52     cout<< ope;
 53     ope.clear(), d = mp[1][s].first, ts = s;
 54     while(d!=-1){
 55         ope.push_back(dir[d]);
 56         ts = mp[1][ts].second;
 57         d = mp[1][ts].first;
 58     }
 59     cout << ope << "\n";
 60 }
 61 void expand(int idx){
 62     static int found = 0;
 63     if(found){
 64         while(!que[idx].empty()) que[idx].pop();
 65         return;
 66     }
 67     int len = que[idx].size();
 68     while(len--){
 69         LL s = que[idx].front(), s2; que[idx].pop();
 70         for(int i=1; i<5; ++i){
 71             decode(s);
 72             int r,c;
 73             if(idx==0)
 74                 r = xx+dx[i], c = xy+dy[i];
 75             else 
 76                 r = xx-dx[i], c = xy-dy[i];
 77             if(r<0 || c<0 || r==3 || c==3)
 78                 continue;
 79             swap(eight[xx][xy], eight[r][c]);
 80             s2 = encode();
 81             if(mp[idx].find(s2)!=mp[idx].end())
 82                 continue;
 83             mp[idx][s2] = make_pair(i,s);
 84             if(mp[idx^1].find(s2)!=mp[idx^1].end()){
 85                 print(s2);
 86                 found=1;
 87                 return ;
 88             }
 89             else que[idx].push(s2);
 90         }
 91     }
 92 }
 93 void dbfs(){
 94     mp[0].clear(), mp[1].clear();
 95     LL tar=8;
 96     for(int i=7; i>0; --i)
 97         tar<<=4, tar |= i;
 98     que[1].push(tar); mp[1][tar]=make_pair(-1,0);// 两者相等??
 99     tar = encode();
100     que[0].push(tar); mp[0][tar] = make_pair(-1,0);
101     while(!que[0].empty() && !que[1].empty()){
102         if(que[0].size()<que[1].size())
103             expand(0);
104         else expand(1);
105     }
106     while(!que[0].empty())
107         expand(0);
108     while(!que[1].empty())
109         expand(1);
110 }
111 int main(){
112     std::ios::sync_with_stdio(false);
113     char c;
114     for(int i=0; i<3; ++i){
115         for(int j=0; j<3; ++j){
116             cin>>c;
117             if(c==‘x‘)
118                 eight[i][j]=0, xx = i, xy = j;
119             else 
120                 eight[i][j]= c-‘0‘;
121         }
122     }
123     int cnt=0; 
124     for(int i=0; i<9; ++i){
125         for(int pi=0; pi<i; ++pi)
126             if(eight[pi/3][pi%3] && eight[pi/3][pi%3]<eight[i/3][i%3])
127                 cnt++;
128     }
129     if(cnt%2)
130         printf("unsolvable\n");
131     else 
132         dbfs();
133     return 0;
134 }