From 704dfb7975c936a199beeaaa907a5784724a8481 Mon Sep 17 00:00:00 2001
From: Kirito <1362050620@qq.com>
Date: Wed, 23 Aug 2017 22:14:40 +0800
Subject: [PATCH] Create 3255.cpp

---
 POJ/3255.cpp | 101 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 POJ/3255.cpp

diff --git a/POJ/3255.cpp b/POJ/3255.cpp
new file mode 100644
index 0000000..ce4b902
--- /dev/null
+++ b/POJ/3255.cpp
@@ -0,0 +1,101 @@
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+#include <vector>
+#include <queue>
+#include <list>
+#include <set>
+#include <map>
+
+#include <algorithm>
+using namespace std;
+
+#define INF 1e9+7
+
+#define MAXN 5000
+#define MAXR 100000
+
+int N,R;
+
+struct edge
+{
+    edge(int To,int Dist):to(To),dist(Dist){}
+
+    int to;
+    int dist;
+};
+
+vector<edge> G[MAXN+1];
+
+/// 最短路: dis[i]=从1号路口出发到i路口的最短距离
+int dis[MAXN+1];
+/// 次短路: second_dis[i]=从1号路口出发到i路口的次短距离
+int second_dis[MAXN+1];
+
+/// PR.first 为距离, PR.second 为点
+typedef pair<int,int> PR;
+
+void solve()
+{
+    priority_queue< PR,vector<PR>,greater<PR> > bus;
+    fill(dis,dis+N,INF);
+    fill(second_dis,second_dis+N,INF);
+
+    dis[0]=0;
+    bus.push(PR(0,0));
+
+    while(!bus.empty())
+    {
+        PR p=bus.top();
+        bus.pop();
+
+        int d=p.first;
+        int v=p.second;
+
+        if(second_dis[v]<d)
+        {
+            /// 如果这个距离比次短路还长，丢弃
+            continue;
+        }
+
+        int sz=G[v].size();
+        for(int i=0;i<sz;i++)
+        {
+            edge& e=G[v][i];
+            int dd=d+e.dist;
+
+            if(dis[e.to]>dd)
+            {
+                /// 如果最短路比新合成距离长，交换(?)
+                swap(dis[e.to],dd);
+                bus.push(PR(dis[e.to],e.to));
+            }
+
+            /// 现在一定有: dd>dis[e.to]
+
+            if(second_dis[e.to] > dd && dis[e.to] < dd)
+            {
+                second_dis[e.to]=dd;
+                bus.push(PR(second_dis[e.to],e.to));
+            }
+        }
+    }
+
+    printf("%d\n",second_dis[N-1]);
+}
+
+int main()
+{
+    scanf("%d %d",&N,&R);
+    for(int i=0;i<R;i++)
+    {
+        int A,B,D;
+        scanf("%d %d %d",&A,&B,&D);
+
+        G[A-1].push_back(edge(B-1,D));
+        G[B-1].push_back(edge(A-1,D));
+    }
+    solve();
+    return 0;
+}