uva-315.network(连通图的割点)

本题大意:求一个无向图额割点的个数.

本题思路:建图之后打一遍模板.

 /*************************************************************************
     > File Name: uva-315.network.cpp
     > Author: CruelKing
     > Mail: 2016586625@qq.com
     > Created Time: 2019年09月06日 星期五 17时15分07秒
     本题思路:就是求图中有多少个割点
  ************************************************************************/

 #include <cstdio>
 #include <iostream>
 #include <sstream>
 #include <cstring>
 #include <string>
 using namespace std;

 const int maxn =  + , maxm = maxn * maxn + ;
 int tot, head[maxn];

 struct Edge {
     int to, next;
 } edge[maxm];

 void init() {
     memset(head, -, sizeof head);
     tot = ;
 }

 void addedge(int u, int v) {
     edge[tot] = (Edge) {v, head[u]}; head[u] = tot ++;
     edge[tot] = (Edge) {u, head[v]}; head[v] = tot ++;
 }    

 int n;
 string str;

 int dfn[maxn], low[maxn], stack[maxn];
 bool cut[maxn], instack[maxn];
 int Index, top, cut_num;

 void tarjan(int u, int pre) {
     dfn[u] = low[u] = ++ Index;
     instack[u] = true;
     stack[top ++] = u;
     int son = ;
     for(int i = head[u]; ~i; i = edge[i].next) {
         int v = edge[i].to;
         if(!dfn[v]) {
             son ++;
             tarjan(v, u);
             if(low[u] > low[v]) low[u] = low[v];
             if(pre != u && low[v] >= dfn[u]) {
                 cut[u] = true;
             }
         } else if(low[u] > dfn[v]) low[u] = dfn[v];
     }
     if(u == pre && son > ) {
         cut[u] = true;
     }
     instack[u] = false;
     top --;
 }

 void solve() {
     memset(dfn, , sizeof dfn);
     memset(low, , sizeof low);
     memset(cut, false, sizeof cut);
     Index = top = cut_num = ;
     for(int i = ; i <= n; i ++) {
         if(!dfn[i]) tarjan(i, i);
     }
     for(int i = ; i <= n; i ++) if(cut[i]) cut_num ++;
     printf("%d\n", cut_num);
 }

 int main() {
     int u, v;
     while(~scanf("%d", &n) && n) {
         init();
         while(scanf("%d", &u)) {
             if(u == ) break;
             getline(cin, str);
             stringstream ss;
             ss << str;
             while(ss >> v) addedge(u, v);
         }
         solve();
     }
     return ;
 }