HDU 4587 two nodes (dual connection cut point application)

Question: N points (0 ~ N-1), m undirected edges, and ask the maximum number of connected parts after removing the two points.

First, remove a vertex to find each cut point, in the DFS process, find out how many connected parts are removed from the cut point (Change iscut [u] = true to iscut [u] ++ ),

In this way, you can find the most connected parts for the second time.

#include<iostream>#include<stdio.h>#include<string.h>#include<string>#include<map>#include<stack>#include<queue>#include<vector>#include<stdlib.h>using namespace std;#define M 5005int pre[M],dfs_clock,iscut[M],low[M],bcc_cnt,bccno[M];vector<int>G[M],bcc[M];struct Edge{    int from,to;}edge[M*2];int edge_num,head[M];void add_edge(int u,int v){    edge[edge_num].from=v;    edge[edge_num].to=head[u];    head[u]=edge_num++;}int del;int dfs(int u,int fa){    int lowu=pre[u]=++dfs_clock;    for(int i=head[u];i!=-1;i=edge[i].to)    {        int v=edge[i].from;        if(v==del) continue;        if(!pre[v])        {            int lowv=dfs(v,u);            lowu=min(lowv,lowu);            if(lowv>=pre[u])                iscut[u]++;        }        else if(pre[v]<pre[u]&&v!=fa)            lowu=min(lowu,pre[v]);    }    if(fa<0) iscut[u]--;    return lowu;}void init(){    dfs_clock=0;    memset(pre,0,sizeof(pre));    memset(iscut,0,sizeof(iscut));    memset(bccno,0,sizeof(bccno));}void find_bcc(int n){    int ans=0;    for(int i=0;i<n;i++)    {        init();        del=i;        int sum=0;        for(int j=0;j<n;j++)        {            if(j!=i&&!pre[j])             {                sum++;                dfs(j,-1);            }        }        int maxcut=-1;        for(int j=0;j<n;j++)        {            if(j!=i)                maxcut=max(maxcut,iscut[j]);        }        ans=max(ans,sum+maxcut);    }    printf("%d\n",ans);}int main(){    int n,m;    while(~scanf("%d%d",&n,&m))    {        int a,b;        edge_num=0;        memset(head,-1,sizeof(head));        while(m--)        {            scanf("%d%d",&a,&b);            add_edge(a,b);            add_edge(b,a);        }        find_bcc(n);    }    return 0;}