This problem does not use the optimal solution.
However, as long as each point is checked, and all reachable positions from that point are marked, it will not be necessary to continue searching later.
To find cycles, an additional array needs to be used to store them.
//====================================================================||
// ||
// ||
// Author : GCA ||
// 6AE7EE02212D47DAD26C32C0FE829006 ||
//====================================================================||
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cctype>
#include <utility>
using namespace std;
#ifdef ONLINE\_JUDGE
#define ll "%lld"
#else
#define ll "%I64d"
#endif
typedef unsigned int uint;
typedef long long int Int;
#define Set(a,s) memset(a,s,sizeof(a))
#define Write(w) freopen(w,"w",stdout)
#define Read(r) freopen(r,"r",stdin)
#define Pln() printf("\\n")
#define I\_de(x,n)for(int i=0;i<n;i++)printf("%d ",x\[i\]);Pln()
#define De(x)printf(#x"%d\\n",x)
#define For(i,x)for(int i=0;i<x;i++)
#define CON(x,y) x##y
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\\
printf("%d ",dp\[htx\]\[hty\]);}Pln();}
#define M 50005
#define PII pair<int,int\>
#define PB push\_back
#define oo INT\_MAX
#define Set\_oo 0x3f
#define Is\_debug true
#define debug(...) if(Is\_debug)printf("DEBUG: "),printf(\_\_VA\_ARGS\_\_)
#define FOR(it,c) for(\_\_typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define eps 1e-6
bool xdy(double x,double y){return x>y+eps;}
bool xddy(double x,double y){return x>y-eps;}
bool xcy(double x,double y){return x<y-eps;}
bool xcdy(double x,double y){return x<y+eps;}
int min3(int x,int y,int z){
int tmp=min(x,y);
return min(tmp,z);
}
int max3(int x,int y,int z){
int tmp=max(x,y);
return max(tmp,z);
}
int n;
int mz\[M\];
bool vis\[M\],vis2\[M\];
int t;
void dfs(int x){
vis\[x\]=vis2\[x\]=1;
if(mz\[x\]!=-1&&!vis2\[mz\[x\]\])dfs(mz\[x\]);
vis2\[x\]=0;
t++;
}
int main() {
ios\_base::sync\_with\_stdio(0);
int test,ff=0;
scanf("%d",&test);
while(test--){
Set(vis,0);
Set(mz,-1);
scanf("%d",&n);
for(int i=0;i<n;i++){
int x,y;
scanf("%d%d",&x,&y);
x--;y--;
mz\[x\]=y;
}
int ans=0,index=-1;
for(int i=0;i<n;i++){
t=0;
if(!vis\[i\])dfs(i);
if(t>ans){
ans=t;
index=i;
}
}
printf("Case %d: %d\\n",++ff,index+1);
}
}