P2136 拉近距离

R53930908

Luogu/problem/P2136/P2136.cpp

@@ -0,0 +1,49 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, m, dist1[1005], dist2[1005], backup[1005];
+
+struct node {
+    int s, t, w;
+} g[10005];
+
+void bellman_ford1() {
+    memset(dist1, 0x3f, sizeof(dist1));
+    dist1[1] = 0;
+    for (int i = 1; i <= n; i++) {
+        memcpy(backup, dist1, sizeof(dist1));
+        for (int j = 1; j <= m; j++) {
+            dist1[g[j].t] = min(dist1[g[j].t], backup[g[j].s] + g[j].w);
+        }
+    }
+}
+
+void bellman_ford2() {
+    memset(dist2, 0x3f, sizeof(dist2));
+    dist2[n] = 0;
+    for (int i = 1; i <= n; i++) {
+        memcpy(backup, dist2, sizeof(dist2));
+        for (int j = 1; j <= m; j++) {
+            dist2[g[j].t] = min(dist2[g[j].t], backup[g[j].s] + g[j].w);
+        }
+    }
+}
+
+int main() {
+    cin >> n >> m;
+    for (int i = 1; i <= m; i++) {
+        cin >> g[i].s >> g[i].t >> g[i].w;
+        g[i].w = -g[i].w;
+    }
+    bellman_ford1();
+    for (int i = 1; i <= m; i++) {
+        if (dist1[g[i].t] > dist1[g[i].s] + g[i].w) {
+            cout << "Forever love" << endl;
+            exit(0);
+        }
+    }
+    bellman_ford2();
+    cout << min(dist1[n], dist2[1]) << endl;
+    return 0;
+}