#1506. Antifloyd（antifloyd）

https://sjzezoj.com/submission/55127

S2OJ/1506/1506.cpp

@@ -0,0 +1,95 @@
+#include <iostream>
+#include <stack>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 205;
+
+int n, ans;
+bool g[N][N], g2[N][N];
+
+// Tarjan
+int cnt, dfn[N], low[N];
+int scc_cnt, id[N], siz[N];
+int dout[N], din[N];
+bool vis[N];
+std::stack<int> st;
+
+void tarjan(int u) {
+    dfn[u] = low[u] = ++cnt;
+    st.push(u);
+    vis[u] = true;
+
+    for (int i = 1; i <= n; i++) {
+        if (!g[u][i]) continue;
+
+        if (!dfn[i]) {
+            tarjan(i);
+            low[u] = std::min(low[u], low[i]);
+        } else if (vis[i]) {
+            low[u] = std::min(low[u], dfn[i]);
+        }
+    }
+
+    if (dfn[u] == low[u]) {
+        scc_cnt++;
+
+        int v;
+        do {
+            v = st.top();
+            st.pop();
+            vis[v] = false;
+            id[v] = scc_cnt;
+            siz[scc_cnt]++;
+        } while (v != u);
+
+        if (siz[scc_cnt] > 1) ans += siz[scc_cnt];
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= n; j++) {
+            cin >> g[i][j];
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        if (!dfn[i]) tarjan(i);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= n; j++) {
+            if (g[i][j] && id[i] != id[j]) {
+                g2[id[i]][id[j]] = true;
+            }
+        }
+    }
+
+    for (int i = 1; i <= scc_cnt; i++) {
+        for (int j = 1; j <= scc_cnt; j++) {
+            for (int k = 1; k <= scc_cnt; k++) {
+                if (i != j && j != k && g2[i][k] && g2[k][j]) {
+                    g2[i][j] = false;
+                }
+            }
+        }
+    }
+
+    for (int i = 1; i <= scc_cnt; i++) {
+        for (int j = 1; j <= scc_cnt; j++) {
+            if (g2[i][j]) ans++;
+        }
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}