【luogu P2324 [SCOI2005]骑士精神】 题解

题目链接：https://www.luogu.org/problemnew/show/P2324

不懂怎么剪枝，所以说，，我需要氧气。。

第一道A*

 // luogu-judger-enable-o2
 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #define maxn 10
 using namespace std;
 int T, ans = , mx, sx, sy;
 int aim[][] = {{,,,,,},
                  {,,,,,},
                  {,,,,,},
                  {,,,,,},
                  {,,,,,},
                  {,,,,,}};
 int dx[] = {-,-,,,,,-,-};
 int dy[] = {,,,,-,-,-,-};
 int a[maxn][maxn];
 inline int h()
 {
     int ret = ;
     for(int i = ; i <= ; i++)
     for(int j = ; j <= ; j++)
     if(a[i][j] != aim[i][j]) ret++;
     return ret;
 }
 inline bool move(int x, int y)
 {
     if(x >=  && x <=  && y >=  && y <= ) return true;
     return false;
 }
 void A_star(int now, int x, int y)
 {
     if(now > mx) return;
     int cnt = h();
     if(cnt == )
     {
         ans = min(ans, now);
         return;
     }
     if(cnt + now -  > mx) return;
     int nowx, nowy;
     for(int i = ; i <= ; i++)
     {
         nowx = x + dx[i];
         nowy = y + dy[i];
         if(move(nowx, nowy))
         {
             swap(a[nowx][nowy],a[x][y]);
             A_star(now+,nowx,nowy);
             swap(a[nowx][nowy],a[x][y]);
         }
     }
 }
 int main()
 {
     cin.sync_with_stdio(false);
     cin>>T;
     while(T--)
     {
         char s;
         ans = ;
         memset(a,,sizeof(a));
         for(int i = ; i <= ; i++)
         for(int j = ; j <= ; j++)
         {
             cin>>s;
             if(s != '*')
             a[i][j] = s +  - '';
             if(s == '*')
             {
                 a[i][j] = ;
                 sx = i;
                 sy = j;
             }
         }
         for(mx = ; mx <= ; mx++)
         {
             A_star(,sx,sy);
             if(ans == mx) break;

         }
         if(ans == )
         {
             cout<<-<<endl;
         }
         else
         {
             cout<<ans<<endl;
         }
     }
     return ;
 }