2017ccpc-final J Hdu-6252 Subway chasing differential constraint

Surface

Test instructions: There are 2 people, all go to the subway, but they have a difference of x minutes, but they have been in the communication, so you know, you in the middle of the AB site, he is in the middle of the CD, (b must be equal to a+1 or a, the same as D), ask you every 2 stations between the time required to meet the Cannot satisfy the output impossible. (Platform from 1 to n,n<=2000)

Puzzle: Typical differential constraints we recall that for inequalities a-b<=x we build (a,b,x);

So for the subject

if (a==b && c==d) {build (d,a,-x); build (b,c,x);}

if (a==b && c!=d) {build (d,a,-x-1); build (b,c,x-1);}

if (a!=b) {build (d,a,-x-1); Build (B,c,x-1);}

In order to ensure the connectivity of the graph, remember to add a super source point, add 1 sides to each point

And the station, the actual problem, each adjacent to 2 stations, at least 1 minutes.

By the way the DFS version of the SPFA board, run fast

1#include <bits/stdc++.h>2 #defineN 20053 #defineM 100054 Const Long Longinf=0x3f3f3f3f3f3f3f3f;5typedefLong LongLLD;6 using namespacestd;7 structRec8 {9     intGo,next;Ten     Long Longv; One }eg[m]; A intHead[n],que[n],nn,k,a,b,c,p,n,du[n]; - LLD Dis[n]; - BOOLUsed[n]; the voidReadint&a) - { -A=0; -     CharC=GetChar (); +      while(c<= +) c=GetChar (); -      while(c> +) a=a*Ten+c-'0', c=GetChar (); + } A voidBuildintAintBLong Longc) at { -p++; -eg[p].go=b; -eg[p].next=Head[a]; -eg[p].v=C; -head[a]=p; in } -stack<int>S; to intSPFA () + { -      for(intI=0; i<=n;i++) the     { * S.push (i); $du[i]=1;Panax Notoginsengused[i]=1; -dis[i]=0; the     } +      while(!s.empty ()) A     { the         intv=s.top (); + S.pop (); -used[v]=0; $          for(intu=head[v];u;u=eg[u].next) $         if(dis[eg[u].go]>dis[v]+eg[u].v) -         { -dis[eg[u].go]=dis[v]+eg[u].v; the             if((++du[eg[u].go]) >nn) -             {Wuyiprintf"Impossible"); the                 return 0 ; -             } Wu             if(!Used[eg[u].go]) S.push (eg[u].go); -         } About     } $     return 1 ; - } - intT,x,d,tt; - intMain () A { +     inttt=0; thescanf"%d",&T); -      while(t--) $     { thep=0; thememset (que,0,sizeof(que)); thememset (Used,0,sizeof(used)); theMemset (Du,0,sizeof(du)); -Memset (Head,0,sizeof(head)); in          while(!S.empty ()) S.pop (); the Read (nn); Read ( k); Read (x); the          for(intI=1; i<=k;i++) About         { the Read ( a); Read (b); Read (c); Read (d) ; the             if(A==b && c==d) the             { +Build (d,a,-x); - build (b,c,x); the}ElseBayi             if(A==b && c!=d) the             { theBuild (d,a,-x-1); -Build (b,c,x-1); -}Else the             { theBuild (d,a,-x-1); theBuild (b,c,x-1); the             } -         } then=nn+1; the          for(intI=1; i<=nn;i++) Build (N,i,0); the          for(intI=1; i<nn;i++) Build (i+1, i,-1);94tt++; theprintf"Case #%d:", TT); the         intwhy=SPFA (); the         if(why) for(intI=2; i<=nn;i++) printf ("%lld", dis[i]-dis[i-1]);98printf"\ n"); About     } -     return 0;101}

2017ccpc-final J Hdu-6252 Subway chasing differential constraint