E 定向 牛客练习赛25

tarjan

父节点和子节点

 #include <cstdio>
 #include <cstdlib>
 #include <cmath>
 #include <cstring>
 #include <time.h>
 #include <string>
 #include <set>
 #include <map>
 #include <list>
 #include <stack>
 #include <queue>
 #include <vector>
 #include <bitset>
 #include <ext/rope>
 #include <algorithm>
 #include <iostream>
 using namespace std;
 #define ll long long
 #define minv 1e-6
 #define inf 1e9
 #define pi 3.1415926536
 #define E  2.7182818284
 const ll mod=1e9+;//
 const int maxn=1e6+;

 struct node
 {
     int d,pos,c;
     node* next;
 }*e[maxn];

 bool vis[maxn]={};
 int dfn[maxn],low[maxn],num=,g=,n,cond[maxn],st[maxn],fa[maxn];

 void dfs(int d)
 {
     int dd;
     node* p=e[d];
     dfn[d]=low[d]=++num;
     vis[d]=;
     st[++g]=d;
     while (p)
     {
         dd=p->d;
         if (!vis[dd])
         {
             fa[dd]=d;
             dfs(dd);
             low[d]=min(low[d],low[dd]);
             cond[p->pos]=p->c;
         }
         //lack whether in stack (not necessarily)
         else if (fa[d]!=dd)
         {
             low[d]=min(low[d],dfn[dd]);
             if (dfn[d]>dfn[dd])
                 cond[p->pos]=p->c;
         }
         p=p->next;
     }
     if (dfn[d]==low[d])
     {
         if (g!=n || st[]!=d)
         {
             printf("impossible");
             exit();
         }
     }
 }

 int main()
 {
     node* p;
     int m,i,x,y;
     scanf("%d%d",&n,&m);
     for (i=;i<=m;i++)
     {
         scanf("%d%d",&x,&y);
         p=(node*) malloc (sizeof(node));
         p->d=y;
         p->pos=i;
         p->c=;
         p->next=e[x];
         e[x]=p;

         p=(node*) malloc (sizeof(node));
         p->d=x;
         p->pos=i;
         p->c=;
         p->next=e[y];
         e[y]=p;
     }
     fa[]=;
     dfs();
     for (i=;i<=m;i++)
         printf("%d",cond[i]);
     return ;
 }
 /*
 3 2
 1 2
 2 3
 */