Problem Link : http://www.lightoj.com/volume_showproblem.php?problem=1034

/*
         +-+ +-+ +-+
         |R| |.| |S|
         +-+ +-+ +-+
 */

#include <bits/stdc++.h>

#define pii             pair <int,int>
#define sc              scanf
#define pf              printf
#define Pi              2*acos(0.0)
#define ms(a,b)         memset(a, b, sizeof(a))
#define pb(a)           push_back(a)
#define MP              make_pair
#define db              double
#define ll              long long
#define EPS             10E-10
#define ff              first
#define ss              second
#define sqr(x)          (x)*(x)
#define D(x)            cout<<#x " = "<<(x)<<endl
#define VI              vector <int>
#define DBG             pf("Hi\n")
#define MOD             100007
#define MAX             10005
#define CIN             ios_base::sync_with_stdio(0); cin.tie(0)
#define SZ(a)           (int)a.size()
#define sf(a)           scanf("%d",&a)
#define sff(a,b)        scanf("%d%d",&a,&b)
#define sfff(a,b,c)     scanf("%d%d%d",&a,&b,&c)
#define loop(i,n)       for(int i=0;i<n;i++)
#define REP(i,a,b)      for(int i=a;i<b;i++)
#define TEST_CASE(t)    for(int z=1;z<=t;z++)
#define PRINT_CASE      printf("Case %d: ",z)
#define all(a)          a.begin(),a.end()
#define intlim          2147483648
#define inf             1000000
#define ull             unsigned long long

using namespace std;

int n,m;
vector<int>graph[MAX],topsort;
bool visited[MAX],test;

void allclear()
{
    loop(i,n+2)
    {
        graph[i].clear();
        visited[i]=0;
    }
    topsort.clear();
}

void dfs(int u)
{
    visited[u]=1;
    loop(i,SZ(graph[u]))
    {
        int v=graph[u][i];
        if(!visited[v])
            dfs(v);
    }
    if(test)
        topsort.pb(u);
}

int main()
{
    ///freopen("in.txt","r",stdin);
    ///freopen("out.txt","w",stdout);
    int t,a,b;
    sf(t);
    TEST_CASE(t)
    {
        sff(n,m);
        loop(i,m)
        {
            sff(a,b);
            graph[a].pb(b);
        }
        test=1;
        int ans=0;
        REP(i,1,n+1)
        {
            if(!visited[i])
                dfs(i);
        }

        test=0;
        loop(i,n+2) visited[i]=0;
        for(int i=SZ(topsort)-1; i>=0; i--)
        {
            int u=topsort[i];
            if(!visited[u])
            {
                dfs(u);
                ans++;
            }
        }
        PRINT_CASE;
        pf("%d\n",ans);
        allclear();
    }
    return 0;
}

Another solution of this problem using Strongly Connected components(SCC) is here…

/*
         +-+ +-+ +-+
         |R| |.| |S|
         +-+ +-+ +-+
 */

#include <bits/stdc++.h>

#define pii             pair <int,int>
#define sc              scanf
#define pf              printf
#define Pi              2*acos(0.0)
#define ms(a,b)         memset(a, b, sizeof(a))
#define pb(a)           push_back(a)
#define MP              make_pair
#define db              double
#define ll              long long
#define EPS             10E-10
#define ff              first
#define ss              second
#define sqr(x)          (x)*(x)
#define D(x)            cout<<#x " = "<<(x)<<endl
#define VI              vector <int>
#define DBG             pf("Hi\n")
#define MOD             100007
#define MAX             10005
#define CIN             ios_base::sync_with_stdio(0); cin.tie(0)
#define SZ(a)           (int)a.size()
#define sf(a)           scanf("%d",&a)
#define sff(a,b)        scanf("%d%d",&a,&b)
#define sfff(a,b,c)     scanf("%d%d%d",&a,&b,&c)
#define loop(i,n)       for(int i=0;i<n;i++)
#define REP(i,a,b)      for(int i=a;i<b;i++)
#define TEST_CASE(t)    for(int z=1;z<=t;z++)
#define PRINT_CASE      printf("Case %d: ",z)
#define all(a)          a.begin(),a.end()
#define intlim          2147483648
#define inf             1000000
#define ull             unsigned long long

using namespace std;

int n,m;
vector<int>graph[MAX],reverse_graph[MAX],scc;
vector<pii>v;
int indegree[MAX],topsort[MAX],finish;
bool visited[MAX];

void allclear()
{
    loop(i,n+2)
    {
        graph[i].clear();
        reverse_graph[i].clear();
        indegree[i]=0;
        visited[i]=0;
        topsort[i];
    }
    scc.clear();
    v.clear();
    finish=0;
}

void dfs1(int u)
{
    finish++;
    visited[u]=1;
    loop(i,SZ(graph[u]))
    {
        int v=graph[u][i];
        if(!visited[v])
            dfs1(v);
    }
    topsort[u]=++finish;
}

void dfs2(int u)
{
    visited[u]=1;
    loop(i,SZ(reverse_graph[u]))
    {
        int v=reverse_graph[u][i];
        if(!visited[v])
            dfs2(v);
    }
}

void dfs3(int u)
{
    visited[u]=1;
    loop(i,SZ(graph[u]))
    {
        int v=graph[u][i];
        if(!visited[v])
            dfs3(v);
    }
}
int main()
{
    ///freopen("in.txt","r",stdin);
    ///freopen("out.txt","w",stdout);
    int t,a,b;
    sf(t);
    TEST_CASE(t)
    {
        sff(n,m);
        loop(i,m)
        {
            sff(a,b);
            graph[a].pb(b);
            reverse_graph[b].pb(a);
            indegree[b]++;
        }

        int ans=0;
        REP(i,1,n+1)
        {
            if(!visited[i])
                dfs1(i);
        }

        REP(i,1,n+1)
        {
            v.pb(MP(topsort[i],i));
        }
        sort(all(v));
        loop(i,n+2)
        visited[i]=0;

        for(int i=SZ(v)-1; i>=0; i--)
        {
            int u=v[i].ss;
            if(!visited[u])
            {
                scc.pb(u);
                dfs2(u);
            }
        }

        loop(i,n+2)
        visited[i]=0;

        loop(i,SZ(scc))
        {
            if(!visited[scc[i]])
            {
                ans++;
                dfs3(scc[i]);
            }
        }
        PRINT_CASE;
        pf("%d\n",ans);
        allclear();
    }
    return 0;
}