poj-3225 Roadblocks (secondary short circuit)

http://poj.org/problem?id=3255

Bessie sometimes visited her friends, but she did not want to go the quickest way home, but wanted to take a short circuit shorter than the shortest way.

The town consists of a two-way road of R, with n junctions. The number is 1 to n, what is the secondary short-circuit length of the intersection of number 1th to n? The secondary short circuit is

A short path shorter than the shortest short length. The same edge can go through multiple times.

A minor short-circuit to a vertex v is either handsome to the other vertex U's shortest path plus the u-v edge, or the short circuit to u, plus the u-v side,

So what is required is the shortest and minor short-circuiting to all vertices, so for each vertex we record more than the minimum distance,

There is a short distance, and then as long as the Dijkstra algorithm with the same approach, constantly update these two distances can be found in the secondary short-circuit.

1 /* ***********************************************2 Author:zch3 Created TIME:2015/5/13 8:16:454 File name:a.cpp5  ************************************************ */6 7#include <cstdio>8#include <cstring>9#include <iostream>Ten#include <algorithm> One#include <vector> A#include <queue> -#include <Set> -#include <map> the#include <string> -#include <cmath> -#include <cstdlib> -#include <ctime> + using namespacestd; - Const intMAXN =5010; + Const intINF =1000000000; A  at intN, R; - structEdge { -     intTo,cost; - Edge () {} -EdgeintXinty) { -to=x; incost=y; -     } to }; +typedef pair<int,int>P; -Vector<edge>G[MAXN]; the intDIST[MAXN]; * intDIST2[MAXN]; $ Panax Notoginseng voidDijkstraints) { -priority_queue<p,vector<p>,greater<p> >que; the      for(intI=0; i<=n;i++) dist[i]=INF; +      for(intI=0; i<=n;i++) dist2[i]=INF; Adist[s]=0; theQue.push (P (0, s)); +  -      while(!Que.empty ()) { $P p=que.top (); Que.pop (); $         intV=p.second, d=P.first; -         if(dist2[v]<d)Continue;//the second short distance of V is smaller than D. -          for(intI=0; I<g[v].size (); + +i) { theEdge e=G[v][i]; -             //cout<<e.to<<endl;Wuyi             intD2=d+E.cost; the             if(DIST[E.TO]&GT;D2) {//Update Shortest distance - swap (DIST[E.TO],D2); Wu Que.push (P (dist[e.to],e.to)); -             } About             if(DIST2[E.TO]&GT;D2&AMP;&AMP;DIST[E.TO]&LT;D2) {//Update secondary short distance $dist2[e.to]=D2; -                 //cout<<d2<<endl; - Que.push (P (dist2[e.to],e.to)); -             } A         } +     } theprintf"%d\n", Dist2[n]); - } $ intMain () the { the     //freopen ("A.txt", "R", stdin); the     //freopen ("B.txt", "w", stdout); the     inta,b,c; -scanf"%d%d",&n,&R); in      for(intI=0; i<r;++i) { thescanf"%d%d%d",&a,&b,&c); the G[a].push_back (Edge (B,c)); About G[b].push_back (Edge (A,c)); the     } theDijkstra1); the     return 0; +}

poj-3225 Roadblocks (secondary short circuit)