#1498. 换乘(transfer)

https://sjzezoj.com/submission/55703

S2OJ/1498/1498.cpp

@@ -0,0 +1,90 @@
+#include <iostream>
+#include <cstring>
+#include <deque>
+#include <set>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1000005;
+
+int n, m, id[N], last[N], dist[N];
+bool vis[N];
+std::set<int> cs;
+std::vector<std::pair<int, int>> c[N], g[N];
+
+void bfs() {
+    memset(dist, 0x3f, sizeof(dist));
+
+    std::deque<int> q;
+
+    dist[1] = 0;
+    q.emplace_back(1);
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop_front();
+
+        if (vis[u]) continue;
+        vis[u] = true;
+
+        for (auto e : g[u]) {
+            int v = e.first,
+                w = e.second;
+
+            if (dist[v] > dist[u] + w) {
+                dist[v] = dist[u] + w;
+
+                if (w) q.emplace_back(v);
+                else q.emplace_front(v);
+            }
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1, u, v, c; i <= m; i++) {
+        cin >> u >> v >> c;
+
+        ::c[c].emplace_back(u, v);
+        cs.insert(c);
+    }
+
+    int cnt = n;
+    for (int x : cs) {
+        for (auto e : c[x]) {
+            int u = e.first,
+                v = e.second;
+
+            if (last[u] != x) {
+                last[u] = x;
+                id[u] = ++cnt;
+                g[u].emplace_back(id[u], 1);
+                g[id[u]].emplace_back(u, 0);
+            }
+
+            if (last[v] != x) {
+                last[v] = x;
+                id[v] = ++cnt;
+                g[v].emplace_back(id[v], 1);
+                g[id[v]].emplace_back(v, 0);
+            }
+
+            g[id[u]].emplace_back(id[v], 0);
+            g[id[v]].emplace_back(id[u], 0);
+        }
+    }
+
+    bfs();
+
+    cout << (dist[n] == 0x3f3f3f3f ? -1 : dist[n]) << endl;
+
+    return 0;
+}