competitive-programming/solved-lightOj/1210.cpp at master · the-redback/competitive-programming · GitHub

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/**
 *                                   ____
 *       ____ ___  ____ ________  __/ __/
 *      / __ `__ \/ __ `/ ___/ / / / /_
 *     / / / / / / /_/ / /  / /_/ / __/
 *    /_/ /_/ /_/\__,_/_/   \__,_/_/
 *
 *    @link : https://the-redback.com
 */
#include <bits/stdc++.h>
using namespace std;

#define ppb       pop_back
#define pb(x)     push_back(x)
#define all(x)    x.begin(), x.end()
#define mem(a, b) memset(a, b, sizeof(a))
#define inf       1000000000
#define eps       1e-9
#define NN        20100

vector<int> arr;
vector<pair<int, int> > e;
vector<int> g[NN], tg[NN];
int view[NN], sinc[NN], source[NN];

int dfs(int u) {
    int i;
    view[u] = 1;
    for (i = 0; i < g[u].size(); i++) {
        if (view[g[u][i]] == 0) dfs(g[u][i]);
    }
    arr.pb(u);
}

int dfs_2nd(int u, int k) {
    int i;
    view[u] = k;
    for (i = 0; i < tg[u].size(); i++) {
        if (view[tg[u][i]] == 0) dfs_2nd(tg[u][i], k);
    }
}

int scc(int n) {
    int i;
    mem(view, 0);
    arr.clear();
    for (i = 1; i <= n; i++)
        if (view[i] == 0) dfs(i);
    mem(view, 0);
    reverse(all(arr));
    int k = 0, l;
    for (i = 0; i < arr.size(); i++)
        if (view[arr[i]] == 0) dfs_2nd(arr[i], k + 1), k++;
    int nodes = k;
    if (nodes <= 1) return 0;
    mem(source, 0);
    mem(sinc, 0);
    int src, si;
    src = si = nodes;
    for (i = 0; i < e.size(); i++) {
        k = e[i].first;
        l = e[i].second;
        if (view[k] != view[l]) {
            if (sinc[view[k]] == 0) si--;
            if (source[view[l]] == 0) src--;

            sinc[view[k]] = 1;
            source[view[l]] = 1;
        }
    }
    return max(src, si);
}

int main() {
    ios_base::sync_with_stdio(false);
    int t = 1, tc;
    cin >> tc;
    int i, j, k, l, m, n;
    while (tc--) {
        cin >> n >> m;

        for (i = 0; i <= n; i++) {
            g[i].clear();
            tg[i].clear();
        }
        e.clear();
        for (i = 0; i < m; i++) {
            cin >> k >> l;
            g[k].pb(l);
            tg[l].pb(k);
            e.pb(make_pair(k, l));
        }
        int nodes = scc(n);
        printf("Case %d: %d\n", t++, nodes);
    }
    return 0;
}