Iron and Coal（3次bfs）

  1 #include <bits/stdc++.h>
  2 using namespace std;
  3 typedef long long ll;
  4 const int maxn = 1e5+10;
  5 const int inf = 0x3f3f3f3f;
  6 const double pi = acos(-1.0);
  7 #define rep(i,first,second) for(ll i=first;i<=second;i++)
  8 #define dep(i,first,second) for(ll i=first;i>=second;i--)
  9 
 10 ll n,m,k;
 11 ll dis[4][maxn],vis[maxn];
 12 vector<ll>g[maxn],ng[maxn];
 13 void bfs1(){
 14     queue<ll>q;
 15     while(!q.empty()) q.pop();
 16     rep(i,1,n+5) vis[i]=0;
 17     q.push(1);
 18     vis[1]=1;
 19     dis[1][1]=0;
 20     while( !q.empty() ){
 21         ll u=q.front(),v;
 22         q.pop();
 23         for(ll i=0;i<g[u].size();i++){
 24             v=g[u][i];
 25             if( vis[v] ) continue;
 26             vis[v]=1;
 27             dis[1][v]=dis[1][u]+1;
 28             q.push(v);
 29         }
 30     }
 31 }
 32 void bfs2(){
 33     queue<ll>q;
 34     while( !q.empty()) q.pop();
 35     rep(i,1,n+5) vis[i]=0;
 36     q.push(n+1);
 37     vis[n+1]=1;
 38     dis[2][n+1]=0;
 39     while( !q.empty() ){
 40         ll u=q.front(),v;
 41         q.pop();
 42         for(ll i=0;i<ng[u].size();i++){
 43             v=ng[u][i];
 44             if( vis[v] ) continue;
 45             if( u==n+1 ) dis[2][v]=dis[2][n+1];
 46             else dis[2][v]=dis[2][u]+1;
 47             vis[v]=1;
 48             q.push(v);
 49         }
 50     }
 51 }
 52 void bfs3(){
 53     queue<ll>q;
 54     while( !q.empty() ) q.pop();
 55     rep(i,1,n+5) vis[i]=0;
 56     q.push(n+2);
 57     vis[n+2]=1;
 58     dis[3][n+2]=0;
 59     while( !q.empty()){
 60         ll u=q.front(),v;
 61         q.pop();
 62         for(ll i=0;i<ng[u].size();i++){
 63             v=ng[u][i];
 64             if( vis[v]) continue;
 65             if( u==n+2 ) dis[3][v]=dis[3][n+2];
 66             else dis[3][v]=dis[3][u]+1;
 67             vis[v]=1;
 68             q.push(v);
 69         }
 70     }
 71 }
 72 
 73 int main()
 74 {
 75     scanf("%lld%lld%lld",&n,&m,&k);
 76     rep(i,1,n) dis[1][i]=dis[2][i]=dis[3][i]=inf;
 77     rep(i,1,m){
 78         ll o;
 79         scanf("%lld",&o);
 80         ng[n+1].push_back(o);
 81     }
 82     rep(i,1,k){
 83         ll c;
 84         scanf("%lld",&c);
 85         ng[n+2].push_back(c);
 86     }
 87     rep(i,1,n){
 88         ll tmp,v;
 89         scanf("%lld",&tmp);
 90         while( tmp-- ){
 91             scanf("%lld",&v);
 92             g[i].push_back(v);
 93             ng[v].push_back(i);
 94         }
 95     }
 96     bfs1();
 97     bfs2();
 98     bfs3();
 99     ll ans=inf;
100     rep(i,1,n){
101         ans=min(ans,dis[1][i]+dis[2][i]+dis[3][i]);
102     }
103     if( ans==inf ) puts("impossible");
104     else{
105         printf("%lld\n",ans);
106     }
107     return 0;
108 }