CF 1051F The Shortest Statement (最短路)

  1 #include <queue>
  2 #include <cstdio>
  3 #include <algorithm>
  4 #include <cstring>
  5 #define ll long long
  6 #define N 100010
  7 #define uint unsigned int
  8 #define inf 0x3f3f3f3f3f3f3fll
  9 using namespace std;
 10 //re
 11 int gint()
 12 {
 13     int ret=0,fh=1;char c=getchar();
 14     while(c<‘0‘||c>‘9‘){if(c==‘-‘)fh=-1;c=getchar();}
 15     while(c>=‘0‘&&c<=‘9‘){ret=(ret<<3)+(ret<<1)+c-‘0‘;c=getchar();}
 16     return ret*fh;
 17 }
 18 
 19 int n,m,cte,num;
 20 int head[N],fa[N];
 21 struct Edge{int to,nxt;ll val;}edge[N*2];
 22 
 23 int find_fa(int x){
 24     int y=x,pre;while(y!=fa[y])y=fa[y];
 25     while(fa[x]!=y){pre=fa[x],fa[x]=y,x=pre;}
 26     return y;
 27 }
 28 void ae(int u,int v,int w){
 29     cte++;edge[cte].to=v,edge[cte].val=w;
 30     edge[cte].nxt=head[u],head[u]=cte;
 31 }
 32 
 33 struct Krus{int x,y,flag;ll val;}e[N];
 34 int cmp(Krus s1,Krus s2){return s1.val<s2.val;}
 35 void Kruskal()
 36 {
 37     int x,y,fx,fy;
 38     for(int i=1;i<=n;i++) fa[i]=i;
 39     sort(e+1,e+m+1,cmp);
 40     for(int i=1;i<=m;i++){
 41         x=e[i].x,y=e[i].y,fx=find_fa(x),fy=find_fa(y);
 42         if(fx!=fy) e[i].flag=1,fa[fy]=fx,ae(x,y,e[i].val),ae(y,x,e[i].val);
 43     }memset(fa,0,sizeof(fa));
 44 }
 45 
 46 int use[N];
 47 struct SBFA{
 48     ll dis[N];int S;
 49     void Main(int s)
 50     {
 51         memset(dis,0x3f,sizeof(dis));
 52         S=s;queue<int>q;q.push(S);
 53         dis[S]=0,use[S]=1;
 54         while(!q.empty()){
 55             int u=q.front();q.pop();
 56             for(int j=head[u];j;j=edge[j].nxt){
 57                 int v=edge[j].to;
 58                 if(dis[v]>dis[u]+edge[j].val){
 59                     dis[v]=dis[u]+edge[j].val;
 60                     if(!use[v]) q.push(v),use[v]=1;
 61                 }
 62             }use[u]=0;
 63         }
 64     }
 65 }sbfa[22];
 66 
 67 ll dis[N];int dep[N],sz[N],son[N],tp[N];
 68 void dfs1(int u,int dad)
 69 {
 70     for(int j=head[u];j;j=edge[j].nxt){
 71         int v=edge[j].to;
 72         if(v==dad) continue;
 73         fa[v]=u,dep[v]=dep[u]+1;
 74         dis[v]=dis[u]+edge[j].val;
 75         dfs1(v,u);sz[u]+=sz[v];
 76         son[u]=sz[v]>sz[son[u]]?v:son[u];
 77     }sz[u]++;
 78 }
 79 void dfs2(int u){
 80     if(son[u]) tp[son[u]]=tp[u],dfs2(son[u]);
 81     for(int j=head[u];j;j=edge[j].nxt){
 82         int v=edge[j].to;
 83         if(v==fa[u]||v==son[u]) continue;
 84         tp[v]=v;dfs2(v);
 85     }
 86 }
 87 int Lca(int x,int y){
 88     while(tp[x]!=tp[y]){
 89         if(dep[tp[x]]<dep[tp[y]]) swap(x,y);
 90         x=fa[tp[x]];
 91     }return dep[x]<dep[y]?x:y;
 92 }
 93 
 94 ll solve(int x,int y){
 95     int lca=Lca(x,y);
 96     ll ans=dis[x]+dis[y]-dis[lca]*2;
 97     for(int i=0;i<num;i++)
 98         ans=min(ans,sbfa[i].dis[x]+sbfa[i].dis[y]);
 99     return ans;
100 }
101 
102 int main()
103 {
104     scanf("%d%d",&n,&m);
105     int x,y;
106     for(int i=1;i<=m;i++)
107         e[i].x=gint(),e[i].y=gint(),e[i].val=gint();
108     Kruskal();
109     dep[1]=1,dfs1(1,-1);
110     tp[1]=1,dfs2(1);
111     for(int i=1;i<=m;i++)
112         if(!e[i].flag){ae(e[i].x,e[i].y,e[i].val),ae(e[i].y,e[i].x,e[i].val);}
113     for(int i=1;i<=m;i++)
114         if(!e[i].flag){sbfa[num].Main(e[i].x),num++;}
115     int q;scanf("%d",&q);
116     for(int i=1;i<=q;i++){
117         x=gint(),y=gint();
118         printf("%I64d\n",solve(x,y));
119     }
120     return 0;
121 }