"UVA1658 Algorithm Competition Primer classic" Admiral "Fee Flow"

Test instructions

Gives a weighted graph of the edge of a V (3<=v<=1000) point E (3<=e<=10000), seeking the path of the two disjoint (except for the point of origin and end point) of the 1-v, which makes the right and the smallest.

Analysis

One of the classic uses of the expense flow is to limit the absence of a common edge, but there is a difference in this question, which limits the absence of a common point. So we take each point out of one side.

The 2 to V-1 each node i is split into I and I ' two nodes, the middle of a capacity of 1, the cost of 0 side. For each edge in the original image (A, A, b), a single arc (a ', a), a capacity of 1, the cost is the weight and then 1 to V for the flow of 2 of the minimum cost flow can be.

1#include <cstdio>2#include <cstring>3#include <algorithm>4#include <iostream>5#include <queue>6 7 using namespacestd;8 Const intmaxn=4000+Ten;9 Const intmaxm=40000+Ten;Ten Const intinf=2147480000; One structmcmf{ A     intHEAD[MAXN],NEXT[MAXM],TO[MAXM], from[MAXM],FLOW[MAXM],CAP[MAXM],COST[MAXM]; -     intINQ[MAXN],D[MAXN],P[MAXN],A[MAXN]; -     intN,m,s,t,sz; the     voidInitintN) { -          This->n=N; -sz=-1; -memset (head,-1,sizeof(head)); +     } -     voidAdd_edge (intAintBintCaintCO) { +++sz; A          from[Sz]=a;to[sz]=b; next[sz]=head[a];head[a]=sz; atcap[sz]=ca;cost[sz]=co;flow[sz]=0; -++sz; -          from[Sz]=b;to[sz]=a; next[sz]=head[b];head[b]=sz; -cap[sz]=ca;cost[sz]=-co;flow[sz]=CA; -     } -     BOOLSPFA (intSintTint&flow,Long Long&Cost ) { in          for(intI=0; i<=n;i++) d[i]=INF; -queue<int>Q; tomemset (INQ,0,sizeof(INQ)); +d[s]=0; inq[s]=1;p [s]=-1; a[s]=INF; - Q.push (s); the          while(!Q.empty ()) { *             intu=Q.front (); Q.pop (); $inq[u]=0;Panax Notoginseng              for(inti=head[u];i!=-1; i=Next[i]) { -                 intv=To[i]; the                 if(cap[i]>flow[i]&&d[v]>d[u]+Cost[i]) { +d[v]=d[u]+Cost[i]; Ap[v]=i; theA[v]=min (a[u],cap[i]-flow[i]); +                     if(!Inq[v]) { -inq[v]=1; $ Q.push (v); $                     } -                 } -             } the         } -         if(D[t]==inf)return false;Wuyiflow+=A[t]; thecost+= (Long Long) a[t]* (Long Long) d[t]; -         intu=T; Wu          while(u!=s) { -flow[p[u]]+=A[t]; Aboutflow[p[u]^1]-=A[t]; $u= from[P[u]]; -         } -         return true; -     } A     Long LongMincost (intSintt) { +         intflow=0; the         Long Longcost=0; -          while(SPFA (S,t,flow,cost)); $         returnCost ; the     } the }MCMF; the intn,m; the intMain () { -      while(SCANF ("%d%d", &n,&m)! =EOF) { in         inta,b,c; theMcmf.init (2*n); the          for(intI=2; i<n;i++){ AboutMcmf.add_edge (I,i+n,1,0); the         } theMcmf.add_edge (1, n+1,2,0); theMcmf.add_edge (N,2*n,2,0); +          for(intI=1; i<=m;i++){ -scanf"%d%d%d",&a,&b,&c); theMcmf.add_edge (A+n,b,1, c);Bayi         } the         intANS=MCMF. Mincost (1,2*n); thecout<<ans<<Endl; -     } - return 0; the}

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"UVA1658 Algorithm Competition Primer classic" Admiral "Fee Flow"