368. 银河

https://www.acwing.com/problem/content/submission/code_detail/9681652/

AcWing/368/368.cpp

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+#include <iostream>
+#include <stack>
+#include <vector>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+const int N = 100005;
+
+int n, m, t, a, b;
+long long ans;
+std::vector<std::pair<int, int>> g[N], g2[N];
+
+// Tarjan
+int cnt, dfn[N], low[N];
+int scc_cnt, id[N], siz[N];
+std::stack<int> st;
+bool vis[N];
+
+void tarjan(int u) {
+    dfn[u] = low[u] = ++cnt;
+    st.push(u);
+    vis[u] = true;
+    for (auto e : g[u]) {
+        int v = e.first;
+        if (!dfn[v]) {
+            tarjan(v);
+            low[u] = std::min(low[u], low[v]);
+        } else if (vis[v]) {
+            low[u] = std::min(low[u], dfn[v]);
+        }
+    }
+    if (low[u] == dfn[u]) {
+        scc_cnt++;
+        int v;
+        do {
+            v = st.top();
+            st.pop();
+            vis[v] = false;
+            id[v] = scc_cnt;
+            siz[scc_cnt]++;
+        } while (v != u);
+    }
+}
+
+// Longest Path
+int dist[N];
+
+int main() {
+    cin >> n >> m;
+    for (int i = 1; i <= n; i++) {
+        g[0].push_back(std::make_pair(i, 1));
+    }
+    for (int i = 1; i <= m; i++) {
+        cin >> t >> a >> b;
+        if (t == 1) {
+            g[a].push_back(std::make_pair(b, 0));
+            g[b].push_back(std::make_pair(a, 0));
+        } else if (t == 2) {
+            g[a].push_back(std::make_pair(b, 1));
+        } else if (t == 3) {
+            g[b].push_back(std::make_pair(a, 0));
+        } else if (t == 4) {
+            g[b].push_back(std::make_pair(a, 1));
+        } else {
+            g[a].push_back(std::make_pair(b, 0));
+        }
+    }
+    tarjan(0);
+    for (int i = 0; i <= n; i++) {
+        for (auto e : g[i]) {
+            if (id[e.first] != id[i]) {
+                g2[id[i]].push_back(std::make_pair(id[e.first], e.second));
+            } else if (e.second) {
+                cout << -1 << endl;
+                exit(0);
+            }
+        }
+    }
+    for (int i = scc_cnt; i > 0; i--) {
+        for (auto e : g2[i]) {
+            int v = e.first,
+                w = e.second;
+            dist[v] = std::max(dist[v], dist[i] + w);
+        }
+    }
+    for (int i = 1; i <= scc_cnt; i++) {
+        ans += 1ll * dist[i] * siz[i];
+    }
+    cout << ans << endl;
+    return 0;
+}