P1807 最长路

R72243775

Luogu/P1807/P1807.cpp

@@ -0,0 +1,50 @@
+#include <cstring>
+#include <iostream>
+#include <queue>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1505,
+          INF = 0x3f3f3f3f;
+
+int n, m, dist[N];
+std::vector<std::pair<int, int>> g[N];
+
+void spfa() {
+    memset(dist, 0xff, sizeof(dist));
+
+    std::queue<int> q;
+    q.push(1);
+    dist[1] = 0;
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        for (auto e : g[u]) {
+            int v = e.first,
+                w = e.second;
+
+            if (dist[v] < dist[u] + w) {
+                dist[v] = dist[u] + w;
+                q.push(v);
+            }
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin >> n >> m;
+    for (int i = 1; i <= m; i++) {
+        int u, v, w;
+        cin >> u >> v >> w;
+        g[u].push_back(std::make_pair(v, w));
+    }
+    spfa();
+    cout << dist[n] << endl;
+    return 0;
+}