Critical Links UVA - 796

题目大意，给出一个无向图，找出所有的桥，按字典序输出即可、

输入的时候注意一下就行了，比较坑，好多空格和单括号

#include <cstdio>  
#include <cstdlib>  
#include <cstring>  
#include <iostream>  
#include <algorithm>  
  
using namespace std;  
  
const int N = 100010;  
const int M = (N * 2);  
  
struct node  
{  
    int next;  
    int to;   
}edge[M];  
  
struct bri  
{  
    int u;  
    int v;  
}bridge[M];     //存储桥的两个端点 
  
int head[N],DFN[N],low[N];   
int Stack[N];  
bool instack[N];  
int tot, stop, _index, scc, cnt;  
  
void init ()  
{  
    memset (head, -1, sizeof(head));  
    memset (DFN, -1, sizeof(DFN));  
    memset (low, 0, sizeof(low));  
    memset (instack, 0, sizeof(instack));  
    tot = stop = cnt = scc = _index = 0;  
}  
  
void addedge (int from, int to)  
{  
    edge[tot].to = to;    
    edge[tot].next = head[from];  
    head[from] = tot++;  
}  
  
int cmp (bri a, bri b)  
{  
    if (a.u == b.u)  
    {  
        return a.v < b.v;  
    }  
    return a.u < b.u;  
}  
  
void tarjan (int u, int pre)  
{  
	int v;
    DFN[u]=low[u]= ++_index;
    instack[u]=true;
    Stack[stop++]=u;
    for(int i=head[u];~i;i=edge[i].next)
    {
    	v=edge[i].to;
    	if(v==pre)
    	{
    		continue;
		}
		if(DFN[v]==-1)
		{
			tarjan(v,u);
			low[u]=min(low[u],low[v]);
			if(DFN[u]<low[v])    //满足桥的条件 
			{
				bridge[++cnt].u=u;
				bridge[cnt].v=v;
				if(bridge[cnt].u>bridge[cnt].v)
				{
					swap(bridge[cnt].u,bridge[cnt].v);
				}
			}
		}
		else if(instack[v])
		{
			low[u]=min(low[u],DFN[v]);
		}	
	}
	if(low[u]==DFN[u])
	{
		scc++;
		do
		{
			v=Stack[--stop];
			instack[v]=false;
		}while(v!=u);
	}
}  
  
void solve (int n)  
{  
    for (int i = 1; i <= n; ++i)  
    {  
        if (DFN[i] == -1)  
        {  
            tarjan(i, -1);  
        }  
    }  
    sort (bridge + 1, bridge + cnt + 1, cmp);  
    printf("%d critical links\n", cnt);  
    for (int i = 1; i <= cnt; ++i)  
    {  
        printf("%d - %d\n", bridge[i].u - 1, bridge[i].v - 1);  
    }  
    printf("\n");  
}  
  
int main()  
{  
	#ifdef LOCAL
		freopen("C:/input.txt", "r", stdin);
	#endif
    int n;  
    int u, v;  
    int num;  
    while (~scanf("%d", &n))  
    {  
        if (n == 0)  
        {  
            printf("0 critical links\n\n");  
            continue;  
        }  
        init();  
        for (int i = 1; i <= n; ++i)  
        {  
            scanf("%d", &u);  
            ++u;  
            getchar();  
            getchar();  
            scanf("%d", &num);  
            getchar();  
            while (num--)  
            {  
                scanf("%d", &v);  
                ++v;  
                addedge (u, v);  
            }  
        }  
        solve (n);  
    }  
    return 0;  
}