UVa 615 - Is It A Tree?

// Accepted

#include<bits/stdc++.h>

using namespace std;

#define fast ios_base::sync_with_stdio(0)
#define bfast cin.tie(0)
#define outs(x) cout << x << " "
#define outn(x) cout << x << "\n"
#define sf scanf
#define pf printf
#define nl puts("")
#define psb push_back
#define mset(c,v) memset(c , v , sizeof c)
#define loop0(n) for(int i=0; i<n; i++)
#define loop1(n) for(int i=1; i<=n; i++)
#define mpair(x , y) make_pair(x , y)
#define all(x) x.begin(), x.end()
#define pi acos(-1.0)
#define psb push_back

typedef unsigned long long ull;
typedef long long LL;
typedef vector<int>vii;
typedef vector<LL>vll;
typedef vector<string>vs;
typedef map<int, int>mpii;
typedef map<string, int>mpsi;
typedef map<char, int>mpci;
typedef map<LL, LL>mpll;

const int mod = 1000007;
const int high = 500;

vii adj[high];
int indegree[high], visited[high] , par[high];

void clr()
{
    for(int i=0; i<high; i++)
    {
        par[i] = 0;
        visited[i] = 0;
        indegree[i] = 0;
        adj[i].clear();
    }
}

void notree()
{
    cout << " is not a tree.\n";
}

void tree()
{
    cout << " is a tree.\n";
}

bool checkIndegree(int cnt)
{
    int i=0;

    for(i=1; i<cnt; i++)
    {
        if(indegree[i] > 1) return false;
    }

    return true;
}

bool checkParent(int cnt)
{
    int pars = 0;

    for(int i=1; i<cnt; i++)
    {
        if(!par[i]) pars+=1;
    }

    if(pars > 1) return false;

    return true;
}

void DFS(int u)
{
    visited[u] = 1;

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

        if(!visited[v])
        {
            DFS(v);
        }
    }
}

int main()
{
    fast;
    mpii mp;
    int i , x , y , a , b , Tc = 0;
    while(cin >> a >> b)
    {
        if(a < 0 && b < 0) break;

        mp.clear();
        clr();

        if(a == 0 && b == 0)
        {
           cout << "Case " << ++Tc;
           tree();
           continue;
        }

        int cnt = 1;

        bool cycle = false;

        if(!mp.count(a))
        {
            mp[a] = cnt++;
        }

        x = mp[a];

        if(!mp.count(b))
        {
            mp[b] = cnt++;
        }

        y = mp[b];

        adj[x].psb(y);

        par[y] = x;

        if(x == y) cycle = true;

        indegree[y]++;

        while(cin >> a >> b)
        {
            if(!a and !b) break;

            if(!mp.count(a))
            {
                mp[a] = cnt++;
            }

            x = mp[a];

            if(!mp.count(b))
            {
                mp[b] = cnt++;
            }

            y = mp[b];

            adj[x].psb(y);

            par[y] = x;

            if(x == y) cycle = true;

            indegree[y]++;
        }

        cout << "Case " << ++Tc;

        if(!cycle)
        {
            bool indegreeOne = checkIndegree(cnt);

            if(!indegreeOne) notree();

            else
            {
                bool parentOne = checkParent(cnt);

                if(!parentOne) notree();

                else
                {
                    int tmpar = 0;

                    for(i=1; i<cnt; i++)
                    {
                        if(!par[i])
                        {
                            tmpar = i;
                            break;
                        }
                    }

                    DFS(tmpar);

                    bool connected = true;

                    for(i=1; i<cnt; i++)
                    {
                        if(!visited[i])
                        {
                            connected = false;
                            break;
                        }
                    }

                    if(connected) tree();
                    else notree();
                }
            }
        }

        else
        {
            notree();
        }
    }

    return 0;
}