851. spfa求最短路

https://www.acwing.com/problem/content/submission/code_detail/7061781/

AcWing/851/851.cpp

@@ -0,0 +1,38 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, m, u, v, w, dist[100005];
+vector<pair<int, int>> g[100005];
+
+void spfa() {
+    memset(dist, 0x3f, sizeof(dist));
+    dist[1] = 0;
+    queue<int> q;
+    q.push(1);
+    while (!q.empty()) {
+        int t = q.front();
+        q.pop();
+        for (auto i : g[t]) {
+            if (dist[i.first] > dist[t] + i.second) {
+                dist[i.first] = dist[t] + i.second;
+                q.push(i.first);
+            }
+        }
+    }
+}
+
+int main() {
+    cin >> n >> m;
+    for (int i = 0; i < m; i++) {
+        cin >> u >> v >> w;
+        g[u].push_back(make_pair(v, w));
+    }
+    spfa();
+    if (dist[n] == 0x3f3f3f3f) {
+        cout << "impossible" << endl;
+    } else {
+        cout << dist[n] << endl;
+    }
+    return 0;
+}