cdoj914-Fang Teacher Fen I "Dijkstra"

http://acm.uestc.edu.cn/#/problem/show/914

Fang Teacher Fen ITime limit:3000/1000ms (java/others) Memory limit:65535/65535kb (java/others)SubmitStatus

The teacher in order to open more lectures, so he was a fen! In the morning he was in one of the classrooms, and then each of them went to each of the different n classrooms (and of course every classroom had a single clone). In the evening, each of the different parts of the classroom, merged into a person (no need to go back at the same time). But the road between classrooms is very rugged and one-way. Of course, even if it is a teacher's fen, that is quite powerful, each one will take the path of the least time. The teacher wanted to know the length of time he spent walking round the longest walk. The topic guarantees a way to go.

Input

Enter three integers in the first lineN,m,x（1≤n≤ ,1≤m≤ ,1≤x≤n ）。 Indicates that there are n classrooms,m Road,x is the place where the teacher is in the square.

NextmRows, three numbers per line,u,v,TShow from the classroomuto the Classroom v has a one-way edge, which takes time t(1≤t≤).

Output

Outputs an integer that takes time for the longest walk of the clone in a round trip.

Sample Input and output

Sample Input	Sample Output
4 8 21 2 41 3 21 4 72 1 12 3 53 1 23 4 44 2 3	10

Dijkstra: two times. The first time along, the second time against. Here the storage of the graph is not suitable for the forward star, suitable for the matrix storage, the reverse side of the time is more convenient.

Code:

1#include <fstream>2#include <iostream>3#include <vector>4#include <queue>5#include <cstring>6#include <cstdio>7 8 using namespacestd;9 Ten Const intinf=0x7fffffff; One Const intn=1005; A Const intm=100005; - intn,m,x; - intA[n][n]; the intDis[n],dis2[n]; - BOOLB[n]; -typedef pair<int,int>PII; -priority_queue<pii,vector<pii>,greater<pii> >p; +  - voidDijkstra (); + voiddijkstra2 (); A  at intMain () - { -     //freopen ("d:\\input.in", "R", stdin); -     //freopen ("D:\\output.out", "w", stdout); -     intT1,t2,t3; -scanf"%d%d%d",&n,&m,&x); in      for(intI=0; i<m;i++){ -scanf"%d%d%d",&t1,&t2,&T3); toa[t1][t2]=T3; +     } - Dijkstra (); the dijkstra2 (); *t1=0; $      for(intI=1; i<=n;i++) T1=max (t1,dis[i]+dis2[i]);Panax Notoginsengprintf"%d\n", T1); -     return 0; the } + voidDijkstra () { A      for(intI=1; i<=n;i++) dis[i]=INF; thedis[x]=0; +P.push (Make_pair (0, x)); -      while(!P.empty ()) { $PII tp=p.top (); $ P.pop (); -         inttx=Tp.second; -         if(B[tx])Continue; theb[tx]=1; -          for(intI=1; i<=n;i++){Wuyi             if(a[tx][i]&& (!B[i])) { the                 if(dis[i]>dis[tx]+A[tx][i]) { -dis[i]=dis[tx]+A[tx][i]; Wu P.push (Make_pair (dis[i],i)); -                 } About             } $         } -     } - } - voidDijkstra2 () { A      for(intI=1; i<=n;i++) dis2[i]=INF; +memset (b,0,sizeof(b)); thedis2[x]=0; -P.push (Make_pair (0, x)); $      while(!P.empty ()) { thePII tp=p.top (); the P.pop (); the         inttx=Tp.second; the         if(B[tx])Continue; -b[tx]=1; in          for(intI=1; i<=n;i++){ the             if(a[i][tx]&& (!B[i])) { the                 if(dis2[i]>dis2[tx]+A[i][tx]) { Aboutdis2[i]=dis2[tx]+A[I][TX]; the P.push (Make_pair (dis2[i],i)); the                 } the             } +         } -     } the}

cdoj914-Fang Teacher Fen I "Dijkstra"