割边

#include <bits/stdc++.h>

using namespace std;

#define INF 0x3f3f3f3f
#define MAXN 1000010
#define MAXM 5010

inline int read()
{
    int x =  0,ff = 1;char ch = getchar();
    while(!isdigit(ch))
    {
        if(ch == '-') ff = -1;
        ch = getchar();
    }
    while(isdigit(ch))
    {
        x = (x << 1) + (x << 3) + (ch ^ 48);
        ch = getchar();
    }
    return x * ff;
}

int n,m,ti = 0,top = 0,dfn[MAXN],low[MAXN],cut[MAXN];
int lin[MAXN],tot = 1;
struct edge
{
    int x,y,next;
}e[MAXN];

inline void add(int xx,int yy)
{
    e[++tot].y = yy;
    e[tot].x = xx;
    e[tot].next = lin[xx];
    lin[xx] = tot;
}

void Tarjan(int x,int bridge)
{
    dfn[x] = low[x] = ++ti;
    for(int i = lin[x],y;i;i = e[i].next)
    {
        if(!dfn[y = e[i].y])
        {
            Tarjan(y,i);
            low[x] = min(low[x],low[y]);
            if(low[y] > dfn[x]) 
                cut[i] = cut[i ^ 1] = true;
        }
        else if(i != (bridge ^ 1)) 
        low[x] = min(low[x],dfn[y]);
    }
}

int main()
{
    n = read(); m = read();
    for(int i = 1;i <= m;++i)
    {
        int x,y;
        x = read(); y = read();
        add(x,y); add(y,x);
    }
    for(int i = 1;i <= n;++i)
    if(!dfn[i]) Tarjan(i,0);
    for(int i = 2;i <= tot;i += 2)
        if(cut[i] == true)
            printf("%d %d
",e[i].x,e[i].y);
　　 return 0;
}