732F Tourist Reform

// CF 732F Tourist Reform
// 思路：两遍tarjan
// 找强联通分量
#include <bits/stdc++.h>
using namespace std;
#define LL long long
typedef pair<int,int> pii;
const int inf = 0x3f3f3f3f;
const int N =41e5+10;
#define clc(a,b) memset(a,b,sizeof(a))
const double eps = 1e-8;
const int MOD = 1e9+7;
void fre() {freopen("in.txt","r",stdin);}
void freout() {freopen("out.txt","w",stdout);}
inline int read() {int x=0,f=1;char ch=getchar();while(ch>'9'||ch<'0') {if(ch=='-') f=-1;ch=getchar();}while(ch>='0'&&ch<='9') {x=x*10+ch-'0';ch=getchar();}return x*f;}

int head[N],low[N],dfn[N],s[N];
int cnt,tot;
struct Edge{
    int v,w,nt;
    Edge(){}
    Edge(int v_,int w_,int nt_):v(v_),w(w_),nt(nt_){}
}e[N<<1];

void add(int u,int v,int w){
    e[cnt]=Edge(v,w,head[u]);
    head[u]=cnt++;
}
pii mat[N];
int rt;
int ans;
void tarjan(int u,int f){
    low[u] = dfn[u] = ++ tot;
    s[++s[0]] = u;
    for(int i = head[u]; i != -1; i = e[i].nt) {
        int v = e[i].v;
        if(v == f) continue;
        if(!dfn[v]) {
            mat[e[i].w] = make_pair(v, u);
            tarjan(v, u);
            low[u] = min(low[u], low[v]);
        }
        else {
            mat[e[i].w] = make_pair(u, v);
            low[u] = min(low[u], dfn[v]);
        }
    }
    if(dfn[u] == low[u]) {
        int res = 1;
        while(s[s[0]] != u) {
            ++ res;
            -- s[0];
        }
        -- s[0];
        if(ans < res) {ans = res; rt = u;}
    }
}

void init(){
    clc(head,-1);
    tot=0;
    cnt=0;
    ans=0;
}
int main(){
    init();
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++){
        int u,v;
        scanf("%d%d",&u,&v);
        add(u,v,i);
        add(v,u,i);
    }
    s[0]=0;
    tarjan(1,-1);
    clc(dfn,0);
    tot=0;
    s[0]=0;
    tarjan(rt,-1);
    printf("%d
",ans);
    for(int i=1;i<=m;i++){
        printf("%d %d
",mat[i].first,mat[i].second);
    }
    return 0;
}