UVa 13038 - Directed Forest

/*

Verdict: Accepted

Solution Technique: Longest/Maximum depth from root

Algorithm used: DFS

*/

#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 = 1e5+3;

vii adj[high];
int indegree[high];

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


int DFS(int u)
{

    int mxdepth = 1 , len = adj[u].size() , depth=0;

    //cout << "u = " << u << " depth = " << depth << "\n";

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

        //cout << "v = " << v << " befor mxdepth = " << mxdepth << "\n";

        depth = DFS(v) + 1;

        //cout << " v =  "  << v << " depth = " << depth << "\n";

        mxdepth = max(depth , mxdepth);

        //cout << "v = " << v << "  mxdepth = " << mxdepth << "\n";
    }

    return mxdepth;
}

int main()
{
    //fast;
    //freopen("out.txt", "w" , stdout);
    int i , u , v , test, tc=0 , N , E , ans=0;
    sf("%d", &test);
    while(test--)
    {
        ans = 0;

        sf("%d %d", &N , &E);

        clr(N);

        for(i=0; i<E; i++)
        {
            sf("%d %d", &u , &v);

            adj[u].psb(v);

            indegree[v]++;
        }

        for(i=1; i<=N; i++)
        {
            if(!indegree[i])
            {

                ans = max(DFS(i) , ans);

                //cout << " maximum = " << ans << "\n";
            }
        }

        pf("Case %d: %d\n", ++tc, ans);
    }

    return 0;
}