LightOj 1003 - Drunk

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<map>
#include<string>
#include<stack>

#define sf scanf
#define pf printf
#define mx 20010
#define white 0
#define gray 1
#define black 2

using namespace std;

typedef map<string, int>mpsi;
typedef vector < vector <int> >vvii;
typedef vector<int>vi;

vi G[mx];
int color[mx];
bool cycle = false;


void graph_clear()
{
    for(int i=0; i<mx; i++)
    {
        G[i].clear();
    }
}

void DFS_Visit(int u)
{
    color[u] = gray;

    int i , v;

    for(i=0; i<G[u].size(); i++)
    {
        v = G[u][i];

        if(color[v] == white)
        {
            DFS_Visit(v);
        }

        else if(color[v] == gray)
        {
            cycle = true;
            return;
        }
    }

    color[u] = black;
}

void DFS(int node)
{
    memset(color, 0, sizeof(color));

    int i;

    for(i=0; i<node; i++)
    {
        if(cycle)
        {
            return ;
        }

        if(color[i] == white)
        {
            DFS_Visit(i);
        }
    }
}

int main()
{
    ios_base::sync_with_stdio(false);
    int t, tc=0;
    mpsi mp;
    cin >> t;
    while(t--)
    {
        mp.clear();
        graph_clear();
        cycle=false;

        int m , i , assin=0 , x , y;
        string s1, s2;

        cin >> m;

        for(i=0; i<m; i++)
        {
            cin >> s1;

            if(mp.find(s1) == mp.end())
            {
                mp[s1] = assin;
                assin++;
            }

            cin >> s2;

            if(mp.find(s2) == mp.end())
            {
                mp[s2] = assin;
                assin++;
            }

            x = mp[s1];
            y = mp[s2];
            G[x].push_back(y);
        }

        DFS(assin);

        cout << "Case " << ++tc << ": ";

        string ans = cycle ? "No" : "Yes";

        cout << ans << "\n";
    }

    return 0;
}