HDU4738 tarjan割边|割边、割点模板

题目：http://acm.hdu.edu.cn/showproblem.php?pid=4738

坑点：

1. 处理重边
2. 图可能不连通，要输出0
3. 若求出的结果是0，则要输出1，因为最少要派一个人

 #include<bits/stdc++.h>
 using namespace std;
 const int maxn = ;
 const int inf = 0x3f3f3f3f;
 struct edge{
     int to,cost;
 };
 vector<edge> g[maxn];
 int num[maxn],low[maxn],index;
 int res;
 int mp[maxn][maxn];//处理两点之间边的条数
 //tarjan
 void tarjan(int cur,int father){
     index++;
     num[cur] = index;
     low[cur] = index;
     for(int i = ;i<g[cur].size();i++){
         if(num[g[cur][i].to] == ){
             tarjan(g[cur][i].to,cur);
             low[cur] = min(low[g[cur][i].to],low[cur]);
             if(low[g[cur][i].to] > num[cur] && mp[cur][g[cur][i].to] == )
                 res = min(res,g[cur][i].cost);
         }else if(g[cur][i].to != father){
             low[cur] = min(low[cur],num[g[cur][i].to]);
         }
     }
 }
 //并查集判断连通性
 int f[maxn];
 int getf(int x){
     if(f[x] == x){
         return x;
     }else{
         return f[x] = getf(f[x]);
     }
 }
 int merge(int l,int r){
     int a = getf(l);
     int b = getf(r);
     if(a != b){
         f[a] = b;
     }
 }
 // 初始化
 void init(int n){
     index = ;
     res = inf;
     memset(num,,sizeof(num));
     memset(low,,sizeof(low));
     memset(mp,,sizeof(mp));
     for(int i = ;i<=n;i++){
         g[i].clear();
         f[i] = i;
     }
 }
 int main(){
     int n,m;
     while(scanf("%d%d",&n,&m) && n && m){
         init(n);
         int a,b,c;
         while(m--){
             scanf("%d%d%d",&a,&b,&c);
             g[a].push_back(edge{b,c});
             g[b].push_back(edge{a,c});
             merge(a,b);
             mp[a][b]++;
             mp[b][a]++;
         }
         int flag = ;
         for(int i = ;i<=n;i++)
             if(getf(i) != getf()){
                 flag = ;
                 break;
             }
         if(flag){
             puts("");
             continue;
         }
         tarjan(,);
         if(res == )
             res++;
         if(res == inf)
             puts("-1");
         else
             printf("%d\n",res);
     }
     return ;
 }  

割边模板：

 #include<bits/stdc++.h>
 using namespace std;
 const int maxn = ;
 const int inf = 0x3f3f3f3f;
 struct edge{
     int to,cost;
 };
 vector<edge> g[maxn];
 int num[maxn],low[maxn],index;
 //tarjan
 void tarjan(int cur,int father){
     index++;
     num[cur] = index;
     low[cur] = index;
     for(int i = ;i<g[cur].size();i++){
         if(num[g[cur][i].to] == ){
             tarjan(g[cur][i].to,cur);
             low[cur] = min(low[g[cur][i].to],low[cur]);
             if(low[g[cur][i].to] > num[cur])
                 //u-v为割边
         }else if(g[cur][i].to != father){
             low[cur] = min(low[cur],num[g[cur][i].to]);
         }
     }
 }
 // 初始化
 void init(int n){
     memset(num,,sizeof(num));
     memset(low,,sizeof(low));
     for(int i = ;i<=n;i++){
         g[i].clear();
     }
 }

割点模板：

 const int maxn = ;
 const int inf = 0x3f3f3f3f;
 struct edge{
     int to,cost;
 };
 vector<edge> g[maxn];
 int num[maxn],low[maxn],index;
 //tarjan
 void tarjan(int cur,int father){
     int child = ;
     index++;
     num[cur] = index;
     low[cur] = index;
     for(int i = ;i<g[cur].size();i++){
         if(num[g[cur][i].to] == ){
             child++;
             tarjan(g[cur][i].to,cur);
             low[cur] = min(low[g[cur][i].to],low[cur]);
             if(low[g[cur][i].to] >= num[cur] && cur!=root)
                 //cur为割点
             if(cur==root && child>=)
                 //cur为割点
         }else if(g[cur][i].to != father){
             low[cur] = min(low[cur],num[g[cur][i].to]);
         }
     }
 }
 // 初始化
 void init(int n){
     memset(num,,sizeof(num));
     memset(low,,sizeof(low));
     for(int i = ;i<=n;i++){
         g[i].clear();
     }
 }