lightoj1003 Drunk

// #pragma comment(linker, "/STACK:1024000000,1024000000")
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <sstream>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <limits.h>
// #define DEBUG
#ifdef DEBUG
#define debug(...) printf( __VA_ARGS__ )
#else
#define debug(...)
#endif
#define MEM(x,y) memset(x, y,sizeof x)
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> ii;
const int inf = 1 << 30;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
map<string,int> mp;
const int maxn = 20010;
int head[maxn], nxt[maxn], to[maxn], tol;
void Add(int u,int v){
to[tol] = v;
nxt[tol] = head[u];
head[u] = tol++;
}
int dfn[maxn], low[maxn];
bool vis[maxn];
int scc;
stack<int> st;
int Time;
void dfs(int u){
vis[u] = true;
dfn[u] = low[u] = Time++;
st.push(u);
for (int i = head[u];i != -1;i = nxt[i]){
int v = to[i];
if (dfn[v] == -1){
dfs(v);
low[u] = min(low[u], low[v]);
}else if (vis[v] && dfn[v] < low[u])
low[u] = dfn[v];
}
if (dfn[u] == low[u]){
scc++;
while(true){
int v = st.top();
st.pop();
vis[v] = false;
if (u == v) break;
}
}
}
int main()
{
// freopen("in.txt","r",stdin);
// freopen("out.txt","w",stdout);
int t;
cin >> t;
int icase = 0;
while(t--){
mp.clear();
int m;
cin >> m;
int cnt = 0;
string a, b;
tol = 0;
MEM(head, -1);
for (int i = 1;i <= m;++i){
cin >> a >> b;
if (!mp[a]) mp[a] = ++cnt;
if (!mp[b]) mp[b] = ++cnt;
Add(mp[a], mp[b]);
}
scc = 0;
MEM(vis, false);
MEM(dfn, -1);
for (int i = 1;i <= cnt;++i){
if (dfn[i] == -1) dfs(i);
}
printf("Case %d: ", ++icase);
if (scc < cnt) puts("No");
else puts("Yes");
}
return 0;
}