ACM/ICPC 之 BFS(离线)+康拓展开 (HDU1430-魔板)

  1 //魔板问题-BFS(离线)+康拓展开
  2 //Time: 38Ms Memory:6484K
  3 #include<iostream>
  4 #include<string>
  5 #include<queue>
  6 #include<algorithm>
  7 using namespace std;
  8 
  9 #define MAX 40321
 10 
 11 int fac[8] = { 1,1,2,6,24,120,720,5040 };    //阶乘数组
 12 
 13 int v[MAX];        //访问标记
 14 string ans[MAX];    //离线表
 15 
 16 struct Board{
 17     int val;    //Hash值
 18     string str;
 19 };
 20 
 21 //康拓展开(Hash)
 22 int Contor(string str)
 23 {
 24     int num = 0;    //Hash值
 25     for (int i = 0; i < 8; i++)
 26     {
 27         int tmp = 0;    //在此后的序列中的位置(升序)
 28         for (int j = i + 1; j < 8; j++)
 29             if (str[j] < str[i]) tmp++;
 30         num += tmp*fac[7 - i];
 31     }
 32     return num;
 33 }
 34 
 35 //离线打表(BFS)
 36 void Init()
 37 {
 38     queue<Board>Q;
 39     Board t, tmp;
 40     t.str = tmp.str = "12345678";    //初始数组
 41     t.val = Contor(t.str);
 42     v[t.val] = 1;
 43     Q.push(t);
 44     while (!Q.empty()) {
 45         t = Q.front();
 46         Q.pop();
 47 
 48         // A:交换行
 49         for (int i = 0; i < 8; i++)
 50             tmp.str[(i + 4) % 8] = t.str[i];
 51 
 52         tmp.val = Contor(tmp.str);
 53         if (!v[tmp.val]) {
 54             v[tmp.val] = 1;
 55             ans[tmp.val] = ans[t.val] + ‘A‘;
 56             Q.push(tmp);
 57         }
 58 
 59         // B:循环右移
 60         for (int i = 0; i < 4; i++)
 61             tmp.str[(i + 1) % 4] = t.str[i];
 62         for (int i = 4; i < 8; i++)
 63             tmp.str[(i + 1) % 4 + 4] = t.str[i];
 64 
 65         tmp.val = Contor(tmp.str);
 66         if (!v[tmp.val]) {
 67             v[tmp.val] = 1;
 68             ans[tmp.val] = ans[t.val] + ‘B‘;
 69             Q.push(tmp);
 70         }
 71 
 72         // C:中心顺时旋转
 73         tmp.str = t.str;
 74         tmp.str[1] = t.str[5]; tmp.str[2] = t.str[1];
 75         tmp.str[6] = t.str[2]; tmp.str[5] = t.str[6];
 76 
 77         tmp.val = Contor(tmp.str);
 78         if (!v[tmp.val]) {
 79             v[tmp.val] = 1;
 80             ans[tmp.val] = ans[t.val] + ‘C‘;
 81             Q.push(tmp);
 82         }
 83     }
 84 }
 85 
 86 int main()
 87 {
 88     Init();    //BFS
 89     string ts, te;
 90     while (cin >> ts >> te)
 91     {
 92         /*转换成顺序魔板*/
 93         swap(ts[5], ts[6]);
 94         swap(ts[4], ts[7]);
 95         swap(te[5], te[6]);
 96         swap(te[4], te[7]);
 97 
 98         /*将起始魔板转换为标准魔板，相应目标魔板也进行变更*/
 99         char tmp[9];
100         for (int i = 0; i < 8; i++)
101             tmp[ts[i] - ‘0‘] = i + ‘1‘;
102         for (int i = 0; i < 8; i++)
103             te[i] = tmp[te[i] - ‘0‘];
104 
105         cout << ans[Contor(te)] << endl;
106     }
107 
108     return 0;
109 }