洛谷P2775 机器人路径规划问题

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题解

至今没看懂这深搜怎么写的……

 //minamoto
 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<queue>
 using namespace std;
 #define getc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
 char buf[<<],*p1=buf,*p2=buf;
 inline int read(){
     #define num ch-'0'
     char ch;bool flag=;int res;
     while(!isdigit(ch=getc()))
     (ch=='-')&&(flag=true);
     for(res=num;isdigit(ch=getc());res=res*+num);
     (flag)&&(res=-res);
     #undef num
     return res;
 }
 #define Nosolution ((n==19)?20:30)
 const int N=;
 int w[N][N];
 inline void add(int u,int v){
     w[u][++w[u][]]=v;
     w[v][++w[v][]]=u;
 }
 int Brk[N],b[N],lca[N][N],d[N],vis[N],p[N],has[N];
 int s,t,n,dep,now;
 queue<int> q;
 void spfa(int s){
     memset(d,0x3f,sizeof(d));
     d[s]=,q.push(s),vis[s]=;
     while(!q.empty()){
         int u=q.front();q.pop();vis[u]=;
         for(int i=;i<=w[u][];++i){
             int v=w[u][i];
             if(d[v]>d[u]+){
                 d[v]=d[u]+,p[v]=u;
                 if(!vis[v]) vis[v]=,q.push(v);
             }
         }
     }
 }
 int cost=;
 bool dfs(int deep){
     if(b[t]==) return true;
     if(deep+lca[now][t]+cost>dep) return false;
     for(int i=;i<=Brk[];++i){
         int u=Brk[i];
         for(int j=;j<=w[u][];++j){
             int v=w[u][j];
             if(!b[v]){
                 Brk[i]=v;
                 if(u==now) now=v;
                 if(has[u]&&!has[v]&&b[u]!=) --cost;
                 if(has[v]&&!has[u]&&b[u]!=) ++cost;
                 swap(b[v],b[u]);
                 if(dfs(deep+)) return true;
                 if(has[u]&&!has[v]&&b[v]!=) ++cost;
                 if(has[v]&&!has[u]&&b[v]!=) --cost;
                 if(now==v) now=u;
                 Brk[i]=u;
                 swap(b[v],b[u]);
             }
         }
     }
     return false;
 }
 int main(){
     //freopen("testdata.in","r",stdin);
     n=read(),s=read(),t=read();
     now=s;
     Brk[++Brk[]]=s;
     for(int i=;i<n;++i){
         b[i]=read()^;
         if(b[i]) Brk[++Brk[]]=i;
         int s,v;
         s=read();
         for(int j=;j<s;++j){
             v=read();
             if(!lca[i][v]&&lca[v][i]){
                 add(i,v);
             }
             lca[i][v]=;
         }
     }
     b[s]=;
     for(int i=;i<n;++i){
         spfa(i);
         for(int j=;j<n;++j) lca[i][j]=d[j];
         if(i==s){
             int u=t;
             while(u!=s){
                 has[u]=;
                 if(b[u]==) ++cost;
                 u=p[u];
             }
             has[s]=;
         }
     }
     for(dep=;dep<=;++dep)
     if(dfs()) return printf("%d\n",dep),;
     printf("%d\n",Nosolution);
     return ;
 }