UVa 11090 going in cycle!! "Bellman_ford"

Test instructions: A weighted graph of n-point m edges is given, and the least-averaged circuit is obtained.

I want to use DFS to find the ring (really too young), in the comparison to find the average weight of each ring, but the code can not be realized, I think it is not right

Later reading = = Good ingenious method, using the dichotomy method, first record the maximum weight of the M-bar UB

Then you can guess a mid, just to determine if there is a loop with an average less than mid, assuming there is a loop with a K-side, the weights for each edge of the loop are w1,w,2,w3,----, wk

So

w1+w2+w3+----+wk<k*mid

And because Lenovo to Bellman_ford can solve the negative ring, the conversion of the above-

(W1-mid) + (W2-mid) + (W3-mid) +----(Wk-mid) <0

This first converts each side W (A, B) into a W (A, B)-mid, and then judges whether there is a negative ring in the "new" graph

When you look at the time there are two do not understand, is the most beginning to judge why to use Ub+1,

is because ub+1 is the worst answer, it can make every side of the most negative, if in this case can not find negative ring, then there must be no negative ring

Then, if the negative ring can be found in the ub+1 condition, then the binary finds the smallest ring of the mean, until it reaches the precision of the loop exit.

Code learning for the standard range = =

1#include <iostream>2#include <cstdio>3#include <cstring>4#include <cmath>5#include <stack>6#include <vector>7#include <map>8#include <Set>9#include <queue>Ten#include <algorithm> One #definemod=1e9+7; A using namespacestd; -  -typedefLong LongLL; the Const intINF =0x7fffffff; - Const intmaxn=10005; -  - structedge{ +     int  from, to; -     DoubleDist; + }; A  at structbellmanford{ -     intn,m; -Vector<edge>edges; -vector<int>G[MAXN]; -     BOOLINQ[MAXN]; -     DoubleD[MAXN]; in     intP[MAXN]; -     intCNT[MAXN]; to      +     voidInitintN) { -          This->n=N; the          for(intI=0; i<n;i++) g[i].clear (); * edges.clear (); $     }Panax Notoginseng      -     voidAddedges (int  from,intTo,DoubleDist) { theEdges.push_back (Edge) { from, to,dist}); +m=edges.size (); Ag[ from].push_back (M-1); the     } +      -     BOOLnegativecycle () { $queue<int>Q; $memset (INQ,0,sizeof(INQ)); -memset (CNT,0,sizeof(CNT)); -          for(intI=0; i<n;i++) {d[i]=0; inq[0]=true; Q.push (i);} the          -          while(!Q.empty ()) {Wuyi             intu=Q.front (); Q.pop (); theinq[u]=false; -              for(intI=0; I<g[u].size (); i++){ Wuedge& e=Edges[g[u][i]]; -                 if(d[e.to]>d[u]+e.dist) { Aboutd[e.to]=d[u]+e.dist; $p[e.to]=G[u][i]; -                     if(!Inq[e.to]) { - Q.push (e.to); -inq[e.to]=true; A                         if(++cnt[e.to]>N) +                         return true; the                     } -                 } $             } the         } the         return false; the     } the }; -  in Bellmanford solver; the  the BOOLTestDoublex) { About      for(intI=0; i<solver.m;i++) thesolver.edges[i].dist-=x; the      the     BOOLret=solver.negativecycle (); +      for(intI=0; i<solver.m;i++) -solver.edges[i].dist+=x; the     returnret;Bayi } the  the intMain () { -     intT; -scanf"%d",&T); the      for(intKase=1; kase<=t;kase++){ the         intn,m; thescanf"%d%d",&n,&m); the solver.init (n); -         intub=0; the          while(m--){ the             intu,v,w; thescanf" %d%d%d", &u,&v,&w); u--;v--;ub=Max (ub,w);94 Solver.            Addedges (U,V,W);  the         } theprintf"Case #%d:", Kase); the         if(!test (ub+1)) printf ("No Cycle found.\n");98         Else{ About             DoubleL=0, r=UB; -              while(r-l>1e-3){101                 Doublem=l+ (r-l)/2;102                 if(Test (M)) R=m;ElseL=M;103             }104printf"%.2lf\n", L); the         }106     }107     return 0;108}

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UVa 11090 going in cycle!! "Bellman_ford"