Uvalive 4839 HDU 3686 traffic Real Time query system

Question:

Find the number of vertices that must pass through from one edge to another in the graph.

Ideas:

The first step must be through the cut point. Therefore, we can first connect the nodes and then contract the point to form a tree. The path on the tree is "non-cut point-not cut ". point-cut point -..." In this mode, the path U-> V only needs to find their LCA, and the answer can be calculated through (DIS [u] + dis [v]-Dis [LCA] * 2)/2.

Note:

This point is reduced by the edge, because it enables each edge to be in a connected block -- by wuyiqi

PS:

The scaled-down part of the Code draws on the SD. The code of the unintentional plug-in feels good to understand orz SD. the unintentional plug-in orz wuyiqi

Code:

#pragma comment(linker, "/STACK:102400000,102400000")#include<cstdio>#include<iostream>#include<string>#include<cstring>#include<algorithm>#include<cmath>#include<map>#include<set>#include<vector>using namespace std;typedef long long LL;#define N 20010#define M 400010#define inf 2147483647int n,m,q,tot,idx,top;int fu[M],fv[M];int head[N],dfn[N],low[N],belong[M],st[M],Tmp[N];int vis[N],dis[N],lca[N][20];struct edge{    int u,v,next;    bool flag;}ed[M];pair<int,int> E[M];void init(){    tot=idx=top=0;    memset(head,-1,sizeof(head));    memset(dfn,-1,sizeof(dfn));    memset(Tmp,0,sizeof(Tmp));    memset(vis,0,sizeof(vis));}void add(int u,int v){    ed[tot].u=u;    ed[tot].v=v;    ed[tot].flag=false;    ed[tot].next=head[u];    head[u]=tot++;}void tarjan(int u,int fa){    int i,j,v;    dfn[u]=low[u]=++idx;    for(i=head[u];~i;i=ed[i].next)    {        v=ed[i].v;        if(ed[i].flag||dfn[v]>=dfn[u]) continue;        ed[i].flag=ed[i^1].flag=true;        st[++top]=i;        if(dfn[v]==-1)        {            tarjan(v,u);            low[u]=min(low[u],low[v]);            if(dfn[u]<=low[v])            {                n++;                do                {                    j=st[top--];                    if(Tmp[ed[j].v]!=n)                    {                        E[m++]=make_pair(n,ed[j].v);                        Tmp[ed[j].v]=n;                    }                    if(Tmp[ed[j^1].v]!=n)                    {                        E[m++]=make_pair(n,ed[j^1].v);                        Tmp[ed[j^1].v]=n;                    }                    belong[j>>1]=n;                }while(j!=i);            }        }        else low[u]=min(low[u],dfn[v]);    }}void maketable(int u,int from){    int i,v;    vis[u]=1;    dis[u]=dis[from]+1;    lca[u][0]=from;    for(i=1;i<20;i++) lca[u][i]=lca[lca[u][i-1]][i-1];    for(i=head[u];~i;i=ed[i].next)    {        v=ed[i].v;        if(v!=from&&!vis[v]) maketable(v,u);    }}int findlca(int u,int v){    if(dis[v]>dis[u]) swap(u,v);    int i,tmp=dis[u]-dis[v];    for(i=19;tmp;i--)    {        if(tmp>=(1<<i))        {            tmp-=(1<<i);            u=lca[u][i];        }    }    if(u==v) return u;    for(i=19;i>=0;i--)    {        if(lca[u][i]!=lca[v][i])        {            u=lca[u][i];            v=lca[v][i];        }    }    return lca[u][0];}int main(){    int i,j,u,v,f;    while(~scanf("%d%d",&n,&m))    {        if(!n&&!m) break;        init();        for(i=1;i<=m;i++)        {            scanf("%d%d",&u,&v);            add(u,v);            add(v,u);            fu[i]=u;            fv[i]=v;        }        m=0;        for(i=1;i<=n;i++)        {            if(dfn[i]==-1) tarjan(i,i);        }        tot=0;        memset(head,-1,sizeof(head));        for(i=0;i<m;i++)        {            add(E[i].first,E[i].second);            add(E[i].second,E[i].first);        }        for(i=1;i<=n;i++)        {            if(!vis[i]) maketable(i,0);        }        scanf("%d",&q);        while(q--)        {            scanf("%d%d",&i,&j);            u=belong[i-1];            v=belong[j-1];            f=findlca(u,v);            printf("%d\n",(dis[u]+dis[v]-dis[f]*2)/2);        }    }    return 0;}

Uvalive 4839 HDU 3686 traffic Real Time query system