边双联通问题求解（构造边双连通图）POJ3352(Road Construction)

题目链接:传送门

题目大意:给你一副无向图,问至少加多少条边使图成为边双联通图

题目思路:tarjan算法加缩点，缩点后求出度数为1的叶子节点个数，需要加边数为(leaf+1)/2

 #include <iostream>
 #include <cstdio>
 #include <cstdlib>
 #include <cmath>
 #include <algorithm>
 #include <cstring>
 #include <stack>
 #include <cctype>
 #include <queue>
 #include <string>
 #include <vector>
 #include <set>
 #include <map>
 #include <climits>
 #define lson root<<1,l,mid
 #define rson root<<1|1,mid+1,r
 #define fi first
 #define se second
 #define ping(x,y) ((x-y)*(x-y))
 #define mst(x,y) memset(x,y,sizeof(x))
 #define mcp(x,y) memcpy(x,y,sizeof(y))
 #define Min(x,y) (x<y?x:y)
 #define Max(x,y) (x>y?x:y)
 using namespace std;
 #define gamma 0.5772156649015328606065120
 #define MOD 1000000007
 #define inf 0x3f3f3f3f
 #define N 5005
 #define maxn 10005
 typedef long long LL;
 typedef pair<int,int> PII;

 vector<int>V[];
 int n,m,hcnt,deep;
 struct Node{
     int to,next;
     Node(){}
     Node(int a,int b):to(a),next(b){}
 }node[N];
 int head[N],vis[N],low[N],dfn[N];
 int d[N];

 inline void add(int x,int y){
     node[hcnt]=Node(y,head[x]);
     head[x]=hcnt++;
 }

 inline void init(){
     mst(d,);
     mst(vis,); vis[]=;
     mst(head,-);
     hcnt=;
     deep=;
     low[]=dfn[]=;
 }

 void dfs(int x,int father){
     for(int i=head[x];~i;i=node[i].next){
         int e=node[i].to;
         if(e==father)continue;
         if(vis[e])low[x]=min(low[x],dfn[e]);
         else{
             vis[e]=;
             low[e]=dfn[e]=++deep;
             dfs(e,x);
             low[x]=min(low[x],low[e]);
         }
     }
 }

 int main(){
     int i,j,group,Case=,x,y;
     while(scanf("%d%d",&n,&m)!=EOF){
         for(i=;i<=n;++i)V[i].clear();
         init();
         while(m--){
             scanf("%d%d",&x,&y);
             add(x,y);
             add(y,x);
             V[x].push_back(y);     ///两点之间联通
             V[y].push_back(x);     ///在缩点之后用于计算度数
         }
         dfs(,-);    ///tarjan算法
         int leaf=;
         for(i=;i<=n;++i)
         if(V[i].size())
         for(j=;j<V[i].size();++j){
             int e=V[i][j];
             if(low[i]!=low[e])
                 d[low[i]]++;
         }
         for(i=;i<=deep;++i)
             if(d[i]==)++leaf;
         printf("%d\n",(leaf+)/);
     }
     return ;
 }