P4878 [USACO05DEC]Layout G

https://www.luogu.com.cn/record/98781737

Luogu/P4878/P4878.cpp

@@ -0,0 +1,90 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+#include <queue>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1005;
+const int INF = 0x3f3f3f3f;
+
+int n, ml, md, cnt[N], dist[N];
+std::vector<std::pair<int, int>> g[N];
+bool vis[N];
+
+bool spfa(int s) {
+    std::fill(std::begin(cnt), std::end(cnt), 0);
+    std::fill(std::begin(vis), std::end(vis), false);
+    std::fill(std::begin(dist), std::end(dist), INF);
+
+    std::queue<int> q;
+
+    q.emplace(s);
+    dist[s] = 0;
+    vis[s] = true;
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        vis[u] = false;
+
+        for (auto e : g[u]) {
+            int v = e.first,
+                w = e.second;
+
+            if (dist[v] > dist[u] + w) {
+                dist[v] = dist[u] + w;
+
+                if (!vis[v]) {
+                    cnt[v] = cnt[u] + 1;
+
+                    if (cnt[v] >= n) return false;
+
+                    vis[v] = true;
+                    q.emplace(v);
+                }
+            }
+        }
+    }
+
+    return true;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> ml >> md;
+
+    for (int i = 1; i <= n; i++) {
+        g[0].emplace_back(i, 0);
+    }
+
+    for (int i = 2; i <= n; i++) {
+        g[i].emplace_back(i - 1, 0);
+    }
+
+    for (int i = 1, a, b, c; i <= ml; i++) {
+        cin >> a >> b >> c;
+
+        g[a].emplace_back(b, c);
+    }
+
+    for (int i = 1, a, b, c; i <= md; i++) {
+        cin >> a >> b >> c;
+
+        g[b].emplace_back(a, -c);
+    }
+
+    if (spfa(0) && spfa(1)) {
+        cout << (dist[n] == INF ? -2 : dist[n]) << endl;
+    } else {
+        cout << -1 << endl;
+    }
+
+    return 0;
+}