From 8d26140581d1981bceef13472f8cb208aff3a6e6 Mon Sep 17 00:00:00 2001
From: Baoshuo <i@baoshuo.ren>
Date: Sat, 1 Jan 2022 20:40:59 +0800
Subject: [PATCH] =?UTF-8?q?P2169=20=E6=AD=A3=E5=88=99=E8=A1=A8=E8=BE=BE?=
 =?UTF-8?q?=E5=BC=8F?=
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R66112607
---
 Luogu/P2169/P2169.cpp | 92 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 Luogu/P2169/P2169.cpp

diff --git a/Luogu/P2169/P2169.cpp b/Luogu/P2169/P2169.cpp
new file mode 100644
index 00000000..7798ef2b
--- /dev/null
+++ b/Luogu/P2169/P2169.cpp
@@ -0,0 +1,92 @@
+#include <iostream>
+#include <limits>
+#include <queue>
+#include <stack>
+#include <vector>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+// Limits
+const int N = 200005;
+
+// Graphs
+int w[N];
+std::vector<std::pair<int, int>> g[N];
+
+// Tarjan
+int cnt, dfn[N], low[N];
+int scc_cnt, id[N];
+std::stack<int> st;
+bool vis[N];
+
+void tarjan(int u) {
+    dfn[u] = low[u] = ++cnt;
+    st.push(u);
+    vis[u] = true;
+    for (auto v : g[u]) {
+        if (!dfn[v.first]) {
+            tarjan(v.first);
+            low[u] = std::min(low[u], low[v.first]);
+        } else if (vis[v.first]) {
+            low[u] = std::min(low[u], dfn[v.first]);
+        }
+    }
+    if (low[u] == dfn[u]) {
+        scc_cnt++;
+        int v;
+        do {
+            v = st.top();
+            st.pop();
+            vis[v] = false;
+            id[v] = scc_cnt;
+        } while (v != u);
+    }
+}
+
+// Shortest Path
+int dist[N];
+
+void spfa() {
+    std::fill(dist, dist + N, 0x3f3f3f3f);
+    std::fill(vis, vis + N, false);
+    std::queue<int> q;
+    q.push(1);
+    dist[1] = 0;
+    vis[1] = true;
+    while (!q.empty()) {
+        auto u = q.front();
+        q.pop();
+        vis[u] = 0;
+        for (auto v : g[u]) {
+            int w = v.second;
+            if (id[u] == id[v.first]) w = 0;
+            if (dist[v.first] > dist[u] + w) {
+                dist[v.first] = dist[u] + w;
+                if (!vis[v.first]) {
+                    q.push(v.first);
+                    vis[v.first] = true;
+                }
+            }
+        }
+    }
+}
+
+int main() {
+    int n, m;
+    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));
+    }
+    for (int i = 1; i <= n; i++) {
+        if (!dfn[i]) {
+            tarjan(i);
+        }
+    }
+    spfa();
+    cout << dist[n] << endl;
+    return 0;
+}