[邻接表DFS]最长链和最大环
http://poj.org/problem?id=3895 (最大环）
http://www.codeforces.com/problemset/problem/116/C （最长链）
两道题，都用的邻接表，这个邻接表上次也说过了，figo教的，next为边内存池吧。。下标和dest与dist对应。最长链就是DFS找到最长的，最深的（DFS每一个点，但是我DFS学的不好，不知道有没有更好的方法，找最大环的时候我刚开始还是用DFS每个点的方法，但是GG了，所以我就研究了一下别人的代码，后来发现不用DFS每一个顶点，只要出现了，DFS条件!vis[i]不满足的情况就说明有环出现，所以只要记录一下子就行了。哦也。
#include<iostream>
#include<cstdio>
#include<iomanip>
#include<algorithm>
#include<cstring>
#include<string>
#include<bitset>
#include<queue>
#include<vector>
#include<string>
#include<cmath>
#include<map>
#define rep(i,n,m) for(int i=(n);i<=(m);++i)
#define re1(i,n) rep(i,1,n)
#define re0(i,n) rep(i,0,n)
#define RE(a) ((a)*(a))
#define SIZE(a) (int((a).size()))
#define vi vector<int>
#define vl vector<ll>
#define vs vector<string>
//time count distance 不能用哦，已经定义了。
using namespace std;
typedef long long ll;
template<class T>
void inline maxi(T &a,const T &b){
a=max(a,b);
}
template<class T>
void inline mini(T &a,const T &b){
a=min(a,b);
}
template<class T>
void show(const T &a,int n,int m){
rep(i,n,m){
cout<<setw(6)<<a[i];
}
cout<<endl;
}
void shownum(int n,int m){
rep(i,n,m){
cout<<setw(6)<<i;
}
cout<<endl;
}
template<class T>
void show(T *a[10],int n,int m){
re0(i,n){
re0(j,m)
cout<<a[i]<<' ';
cout<<endl;
}
}
template<class T,class P>
void fill(T &a,P v){
re0(i,SIZE(a)-1)
a[i]=v;
}
const int maxnum=2000+1;
const int maxint=2147483647;
vi G,next,dist,dest,path,d;
vector<bool> vis;
void addD(int from,int to,int dis=1){
next.push_back(G[from]);
G[from]=SIZE(next)-1;
dest.push_back(to);
dist.push_back(dis);
}
int timee,n;
void init(){
G.assign(maxnum,-1);
scanf("%d",&n);
re1(u,n){
int a;
scanf("%d",&a);
if(a!=-1)
addD(u,a);
}
vis.assign(maxnum,false);
path.assign(maxnum,-1);
d.assign(maxnum,-1);
}
void dfs(int s){
vis[s]=true;
timee++;
d[s]=timee;
for(int i=G[s];i!=-1;i=next[i]){
int v=dest[i];
if(!vis[v]){
path[v]=s;
dfs(v);
}
}
}
/*
int findp(int from,int to){
if(to==-1)
return -1;
if(from!=path[to])
return findp(from,path[to]);
}
void print_path(int from,int to){
if(to==from){
cout<<from<<endl;
}else if(path[to]==-1){
cout<<"GG"<<endl;
}else{
print_path(from,path[to]);
cout<<to<<endl;
}
}
*/
int mmain(){
init();
/*
shownum(0,n);
show(G,0,n);
show(next,0,SIZE(next)-1);
show(dest,0,SIZE(next)-1);
*/
int ans=-1;
re1(u,n){
timee=0;
fill(vis,false);
if(!vis[u])
dfs(u);
maxi(ans,timee);
}
cout<<ans<<endl;
/*
if(findp(5,6)!=-1){
print_path(5,6);
}else
cout<<"GG"<<endl;
*/
}
#define codeforces CODEFORCES
//#define INPUT CODEFORCES_FILE
//#define MANY_TEST CODEFORCES_MANY_TEST
int main(){
#ifdef codeforces
#ifdef INPUT
freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);
#endif
#ifdef MANY_TEST
re1(wwwwwwwwwwwwwwwwwwwww,3)
mmain();
return 0;
#endif
#endif
mmain();
#include<cstdio>
#include<iomanip>
#include<algorithm>
#include<cstring>
#include<string>
#include<bitset>
#include<queue>
#include<vector>
#include<string>
#include<cmath>
#include<map>
#define rep(i,n,m) for(int i=(n);i<=(m);++i)
#define re1(i,n) rep(i,1,n)
#define re0(i,n) rep(i,0,n)
#define RE(a) ((a)*(a))
#define SIZE(a) (int((a).size()))
#define vi vector<int>
#define vl vector<ll>
#define vs vector<string>
//time count distance 不能用哦，已经定义了。
using namespace std;
typedef long long ll;
template<class T>
void inline maxi(T &a,const T &b){
a=max(a,b);
}
template<class T>
void inline mini(T &a,const T &b){
a=min(a,b);
}
template<class T>
void show(const T &a,int n,int m){
rep(i,n,m){
cout<<setw(6)<<a[i];
}
cout<<endl;
}
void shownum(int n,int m){
rep(i,n,m){
cout<<setw(6)<<i;
}
cout<<endl;
}
template<class T>
void show(T *a[10],int n,int m){
re0(i,n){
re0(j,m)
cout<<a[i]<<' ';
cout<<endl;
}
}
template<class T,class P>
void fill(T &a,P v){
re0(i,SIZE(a)-1)
a[i]=v;
}
const int maxnum=2000+1;
const int maxint=2147483647;
vi G,next,dist,dest,path,d;
vector<bool> vis;
void addD(int from,int to,int dis=1){
next.push_back(G[from]);
G[from]=SIZE(next)-1;
dest.push_back(to);
dist.push_back(dis);
}
int timee,n;
void init(){
G.assign(maxnum,-1);
scanf("%d",&n);
re1(u,n){
int a;
scanf("%d",&a);
if(a!=-1)
addD(u,a);
}
vis.assign(maxnum,false);
path.assign(maxnum,-1);
d.assign(maxnum,-1);
}
void dfs(int s){
vis[s]=true;
timee++;
d[s]=timee;
for(int i=G[s];i!=-1;i=next[i]){
int v=dest[i];
if(!vis[v]){
path[v]=s;
dfs(v);
}
}
}
/*
int findp(int from,int to){
if(to==-1)
return -1;
if(from!=path[to])
return findp(from,path[to]);
}
void print_path(int from,int to){
if(to==from){
cout<<from<<endl;
}else if(path[to]==-1){
cout<<"GG"<<endl;
}else{
print_path(from,path[to]);
cout<<to<<endl;
}
}
*/
int mmain(){
init();
/*
shownum(0,n);
show(G,0,n);
show(next,0,SIZE(next)-1);
show(dest,0,SIZE(next)-1);
*/
int ans=-1;
re1(u,n){
timee=0;
fill(vis,false);
if(!vis[u])
dfs(u);
maxi(ans,timee);
}
cout<<ans<<endl;
/*
if(findp(5,6)!=-1){
print_path(5,6);
}else
cout<<"GG"<<endl;
*/
}
#define codeforces CODEFORCES
//#define INPUT CODEFORCES_FILE
//#define MANY_TEST CODEFORCES_MANY_TEST
int main(){
#ifdef codeforces
#ifdef INPUT
freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);
#endif
#ifdef MANY_TEST
re1(wwwwwwwwwwwwwwwwwwwww,3)
mmain();
return 0;
#endif
#endif
mmain();
}
#include<iostream>
#include<cstdio>
#include<iomanip>
#include<algorithm>
#include<cstring>
#include<string>
#include<bitset>
#include<queue>
#include<vector>
#include<string>
#include<cmath>
#include<map>
#define rep(i,n,m) for(int i=(n);i<=(m);++i)
#define re1(i,n) rep(i,1,n)
#define re0(i,n) rep(i,0,n)
#define re(a) ((a)*(a))
#define SIZE(a) (int((a).size()))
#define v(a) vector<a>
#define vi v(int)
#define vl v(ll)
#define vb v(bool)
//count distance 不能用哦，已经定义了。
using namespace std;
typedef long long ll;
template<class T>
void inline maxi(T &a,const T &b){
a=max(a,b);
}
template<class T>
void inline mini(T &a,const T &b){
a=min(a,b);
}
template<class t,class p>
void fill(t &a,p v){
int n=SIZE(a)-1;
re0(i,n)
a[i]=v;
}
void shownum(int n,int m){
rep(i,n,m){
cout<<setw(6)<<i;
}
cout<<endl;
}
template<class t>
void show(t &a,int n,int m){
rep(i,n,m){
cout<<setw(6)<<a[i];
}
cout<<endl;
}
template<class t>
void show(t *a[10],int n,int m){
re0(i,n){
re0(j,m)
cout<<a[i]<<' ';
cout<<endl;
}
}
const int maxnum=4444+1;
const int maxint=2147483647;
int n,m,ans;
vi G,next,dest,d,timee;
vb vis;
void addd(int from,int to){
next.push_back(G[from]);
G[from]=SIZE(next)-1;
dest.push_back(to);
}
void init(){
scanf("%d%d",&n,&m);
G.assign(n+1,-1);
vis.assign(n+1,false);
d.assign(n+1,1);
timee.assign(n+1,0);
re1(u,m){
int a,b;
scanf("%d%d",&a,&b);
addd(a,b);
addd(b,a);
}
}
void findl(int s,int time){
vis[s]=true;
timee[s]=time;
for(int i=G[s];i!=-1;i=next[i]){
int v=dest[i];
if(!vis[v]){
findl(v,time+1);
}else{
maxi(ans,timee[v]-timee[s]);
}
}
}
int mmain(){
int tcase;
scanf("%d",&tcase);
re1(uuuuuuuuuuuuuuu,tcase){
init();
ans=-1;
/*
shownum(0,size(next)-1);
show(g,0,n);
show(next,0,size(next)-1);
show(dest,0,size(next)-1);
*/
re1(u,n){
if(!vis[u])
findl(u,1);
}
printf("%d\n",ans+1);
}
}
//#define codeforces codeforces
//#define input codeforces_file
//#define many_test codeforces_many_test
int main(){
#ifdef codeforces
#ifdef input
freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);
#endif
#ifdef many_test
re1(wwwwwwwwwwwwwwwwwwwww,3)
mmain();
return 0;
#endif
#endif
mmain();
#include<iomanip>
#include<algorithm>
#include<cstring>
#include<string>
#include<bitset>
#include<queue>
#include<vector>
#include<string>
#include<cmath>
#include<map>
#define rep(i,n,m) for(int i=(n);i<=(m);++i)
#define re1(i,n) rep(i,1,n)
#define re0(i,n) rep(i,0,n)
#define re(a) ((a)*(a))
#define SIZE(a) (int((a).size()))
#define v(a) vector<a>
#define vi v(int)
#define vl v(ll)
#define vb v(bool)
//count distance 不能用哦，已经定义了。
using namespace std;
typedef long long ll;
template<class T>
void inline maxi(T &a,const T &b){
a=max(a,b);
}
template<class T>
void inline mini(T &a,const T &b){
a=min(a,b);
}
template<class t,class p>
void fill(t &a,p v){
int n=SIZE(a)-1;
re0(i,n)
a[i]=v;
}
void shownum(int n,int m){
rep(i,n,m){
cout<<setw(6)<<i;
}
cout<<endl;
}
template<class t>
void show(t &a,int n,int m){
rep(i,n,m){
cout<<setw(6)<<a[i];
}
cout<<endl;
}
template<class t>
void show(t *a[10],int n,int m){
re0(i,n){
re0(j,m)
cout<<a[i]<<' ';
cout<<endl;
}
}
const int maxnum=4444+1;
const int maxint=2147483647;
int n,m,ans;
vi G,next,dest,d,timee;
vb vis;
void addd(int from,int to){
next.push_back(G[from]);
G[from]=SIZE(next)-1;
dest.push_back(to);
}
void init(){
scanf("%d%d",&n,&m);
G.assign(n+1,-1);
vis.assign(n+1,false);
d.assign(n+1,1);
timee.assign(n+1,0);
re1(u,m){
int a,b;
scanf("%d%d",&a,&b);
addd(a,b);
addd(b,a);
}
}
void findl(int s,int time){
vis[s]=true;
timee[s]=time;
for(int i=G[s];i!=-1;i=next[i]){
int v=dest[i];
if(!vis[v]){
findl(v,time+1);
}else{
maxi(ans,timee[v]-timee[s]);
}
}
}
int mmain(){
int tcase;
scanf("%d",&tcase);
re1(uuuuuuuuuuuuuuu,tcase){
init();
ans=-1;
/*
shownum(0,size(next)-1);
show(g,0,n);
show(next,0,size(next)-1);
show(dest,0,size(next)-1);
*/
re1(u,n){
if(!vis[u])
findl(u,1);
}
printf("%d\n",ans+1);
}
}
//#define codeforces codeforces
//#define input codeforces_file
//#define many_test codeforces_many_test
int main(){
#ifdef codeforces
#ifdef input
freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);
#endif
#ifdef many_test
re1(wwwwwwwwwwwwwwwwwwwww,3)
mmain();
return 0;
#endif
#endif
mmain();
}
