ZOJ 2588 Burning Bridges 求割边

求割边，实际上跟求割点类似，dfs的过程中就能求出割边，判断条件变为low[v] > dfn[u]和(u,v)不能是重边

我用的邻接表存储，结构体中新增的一个变量，用来判断是否有重边

每次插入边之前先扫描一遍该点的邻接点，看是否已经存在一个边

/*
ID: sdj22251
PROG: subset
LANG: C++
*/
#include <iostream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cmath>
#include <ctime>
#define LOCA
#define MAXN 10005
#define INF 100000000
#define eps 1e-7
using namespace std;
struct node
{
    int v, w, id;
    node *next;
} edge[MAXN];
int visited[MAXN];
int n, m;
int tmpdfn;
int dfn[MAXN];
int low[MAXN];
int ans[200005];
int cnt;
void dfs(int u, int father)
{
    node *ptr = edge[u].next;
    while(ptr)
    {
        int v = ptr -> v;
        if(!visited[v])
        {
            visited[v] = 1;
            tmpdfn++;
            dfn[v] = low[v] = tmpdfn;
            dfs(v, u);
            low[u] = min(low[u], low[v]);
            if(low[v] > dfn[u] && ptr -> w == 0)
            {
                ans[cnt++] = ptr -> id;
            }
        }
        else if(v != father)
        {
            low[u] = min(low[u], dfn[v]);
        }
        ptr = ptr -> next;
    }
}
void init()
{
    low[1] = dfn[1] = 1;
    tmpdfn = 1;
    cnt = 0;
    memset(visited, 0, sizeof(visited));
    visited[1] = 1;
    for(int i = 0; i <= n; i++)
    {
        edge[i].w = 0;
        edge[i].next = NULL;
    }
}
void insert(const int &x, const int &y, const int &id)
{
    node *ptr = edge[x].next;
    bool flag = false;
    while(ptr)
    {
        if(ptr -> v == y)
        {
            ptr -> w = 1;
            flag = true;
        }
        ptr = ptr -> next;
    }
    if(!flag)
    {
        node *pptr = new node;
        pptr -> v = y;
        pptr -> id = id;
        pptr -> w = 0;
        pptr -> next = edge[x].next;
        edge[x].next = pptr;
    }
}
int main()
{
    int T, x, y, cas = 0;
    scanf("%d", &T);
    while(T--)
    {
        if(cas++) printf("\n");
        scanf("%d%d", &n, &m);
        init();
        for(int i = 1; i <= m; i++)
        {
            scanf("%d%d", &x, &y);
            insert(x, y, i);
            insert(y, x, i);
        }
        dfs(1, 0);
        printf("%d\n", cnt);
        sort(ans, ans + cnt);
        for(int i = 0; i < cnt - 1; i++)
        printf("%d ", ans[i]);
        if(cnt) printf("%d\n", ans[cnt - 1]);
    }
    return 0;
}