hihoCoder#1054 滑动解锁

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对于每个待枚举的点，检查：

1. 度数检查：是否违反了出度入度限制。因为生成的路径除了首尾节点外，其他节点的出度和入度只能为2

2. 共线检查：是否违反了共线条件。即跨越了尚未枚举过的节点

对于枚举产生的路径，检查：

1. 长度检查：长度是否大于等于4

2. 完整性检查：是否包含了片段中出现的所有边

代码：

 #include <iostream>
 #include <cstring>

 using namespace std;

 int impossible[];

 bool integrity_check(int piece[][], int path[][]) {
   for (int i = ; i < ; i++)
     for (int j = ; j < ; j++)
         if (piece[i][j] && !path[i][j])
           return false;
   return true;
 }

 bool degree_check(int piece[][], int path[][], int b, int e) {
   if (piece[b][e])
     return true;

   int bdegree = ;
   int edegree = ;

   for (int i = ; i < ; i++) {
     bdegree += path[b][i] || piece[b][i] ?  : ;
     edegree += path[e][i] || piece[e][i] ?  : ;
   }

   return bdegree <  && edegree < ;
 }

 bool collineation_check(int visited[], int b, int e) {
   int t = (b + ) *  + e + ;
   return impossible[t] <  || visited[impossible[t] - ];
 }

 bool check(int piece[][], int path[][], int visited[], int b, int e) {
   if (visited[e])
     return false;

   return degree_check(piece, path, b, e) && collineation_check(visited, b, e);
 }

 int search(int piece[][], int path[][], int visited[], int p, int len) {
   int res = ;

   if (len >=  && integrity_check(piece, path))
     res++;

   for (int i = ; i <  && len < ; i++) {
     if (check(piece, path, visited, p, i)) {
       visited[i] = ;
       path[p][i] = path[i][p] = ;
       res += search(piece, path, visited, i, len + );
       path[p][i] = path[i][p] = ;
       visited[i] = ;
     }
   }

   return res;
 }

 int main() {
   int T;
   memset(impossible, -, sizeof(int) * );
   impossible[] = ;
   impossible[] = ;
   impossible[] = ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;
   impossible[]= ;

   cin >> T;
   while (T--) {
     int N;
     int piece[][] = {{, }};
     int path[][] = {{, }};
     int visited[] = {};
     int res = ;

     cin >> N;
     for (int i = ; i < N; i++) {
       int a, b;
       cin >> a >> b;
       piece[a - ][b - ] = piece[b - ][a - ] = ;
     }

     for (int i = ; i < ; i++) {
       visited[i] = ;
       res += search(piece, path, visited, i, );
       visited[i] = ;
     }

     cout << res << endl;
   }
   return ;
 }