#1991. 【模板】缩点

https://sjzezoj.com/submission/74866

S2OJ/1991/1991.cpp

@@ -0,0 +1,114 @@
+#include <iostream>
+#include <algorithm>
+#include <queue>
+#include <stack>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e4 + 5;
+const int INF = 0x3f3f3f3f;
+
+int n, m, a[N];
+std::vector<int> g[N], g2[N];
+int cnt, dfn[N], low[N];
+int scc_cnt, id[N], w[N], dist[N];
+bool vis[N];
+std::stack<int> st;
+
+void tarjan(int u) {
+    dfn[u] = low[u] = ++cnt;
+    vis[u] = true;
+    st.push(u);
+
+    for (int v : g[u]) {
+        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;
+            w[scc_cnt] += a[v];
+        } while (v != u);
+    }
+}
+
+int spfa(int s) {
+    std::fill_n(dist, N, -INF);
+
+    int res = 0;
+    std::queue<int> q;
+
+    q.emplace(s);
+    dist[s] = 0;
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        res = std::max(res, dist[u] + w[u]);
+
+        for (int v : g2[u]) {
+            if (dist[v] < dist[u] + w[u]) {
+                dist[v] = dist[u] + w[u];
+                q.push(v);
+            }
+        }
+    }
+
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    for (int i = 1, u, v; i <= m; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        if (!dfn[i]) {
+            tarjan(i);
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int v : g[i]) {
+            if (id[i] != id[v]) {
+                g2[id[i]].emplace_back(id[v]);
+            }
+        }
+    }
+
+    int ans = 0;
+
+    for (int i = 1; i <= scc_cnt; i++) {
+        ans = std::max(ans, spfa(i));
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}

S2OJ/1991/resources/gen.cpp

@@ -0,0 +1,57 @@
+/**
+ * @file S2OJ/1991/gen.cpp
+ * @author Baoshuo <i@baoshuo.ren>
+ * @url https://baoshuo.ren
+ * @license GPL-3.0
+ * @date 2023-03-30
+ */
+
+#include "testlib.h"
+
+#include <iostream>
+#include <limits>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+#define N_TESTS 20
+#define PERCENT_TESTS(_percent) (static_cast<double>(_percent) / 100 * N_TESTS)
+
+int main(int argc, char* argv[]) {
+    registerGen(argc, argv, 1);
+
+    int id = opt<int>("id");
+
+    int min_n = 10000,
+        max_n = 10000;  // 1e4
+    int min_m = 10000,
+        max_m = 10000;  // 1e4
+
+    if (id <= PERCENT_TESTS(50)) {
+        min_n = max_n = 100;
+        min_m = max_m = 100;
+    } else {  // all tests
+        // (none)
+    }
+
+    int n = rnd.next(min_n, max_n);
+    int m = rnd.next(min_m, max_m);
+
+    cout << n << ' ' << m << endl;
+
+    for (int i = 1; i <= n; i++) {
+        const char end_c = i < n ? ' ' : '\n';
+
+        cout << rnd.next(0, 1000) << end_c;
+    }
+
+    for (int i = 1; i <= m; i++) {
+        int u = rnd.next(1, n);
+        int v = rnd.next(1, n);
+
+        cout << u << ' ' << v << endl;
+    }
+
+    return 0;
+}