POJ 2983:is The information Reliable? (differential constraint)

The main topic: There are n points in a straight line, there are two types of relationship: P (x,y,v) means x at the north side of the V distance, V (x, y) means X at the north of the Y at least 1 distance out, give some of these relationships, to determine whether there is contradiction.

Analysis:

The differential constrained template problem, the constraint condition p:a-b>=v a-b<=v namely A-b>=v b-a<=-v,v:a-b>=1 namely B-a<=-1, the composition SPFA judgment negative right loop can.

It is important to note that a two-dimensional array can not be used for the storage of images, as there will be multiple edges between two points. 、

Spfa the method of judging the negative right loop, record the number of each point into the team, the number of points exceeds the existence of negative right loop.

Code:

 Programinfor;type Point=^node; Node=Recordx,len:longint; next:point; End;varA:Array[0.. +] ofPoint ; Q:Array[0..500000] ofLongint; Dis,vis:Array[0.. +] ofLongint; G:Array[0.. +] ofBoolean;  N,i,m,x,y,v:longint;  C:char; P:point;procedureput (x,y,v:longint);varP:point;beginnew (P); p^.x:=x; P^.len:=v; p^.next:=a[y];a[y]:=p;End;proceduregetnew;varI:longint;beginFillchar (q,sizeof (q),0); Fillchar (G,sizeof (g), false); Fillchar (vis,sizeof (VIS),0);  fori:=1  toN DoDis[i]:=maxlongintDiv 3;  fori:=0  toN Do beginDispose (A[i]); New (A[i]); a[i]:=Nil;End; dis[0]:=0; g[0]:=true; q[1]:=0;End;functionSpfa:boolean;varx,y,h,t:longint; p:point;beginh:=0; t:=1;  whileH<t Do   beginInc (H); x:=Q[H]; G[x]:=false; New (P);p: =A[x];  whileP<>Nil  Do      beginy:=p^.x; ifDis[x]+p^.len<dis[y] Then          beginDis[y]:=dis[x]+P^.len; ifG[y]=false Then              beginInc (T); Q[t]:=y; g[y]:=true; End; Inc (Vis[y]); ifVis[y]>n Thenexit (FALSE); End; P:=P^.next; End; End; Exit (true);End;beginreadln (n,m);  while(n<>0)or(m<>0) Do   begingetnew;  fori:=1  toN DoPut (I,0,0);  fori:=1  toM Do      beginread (c); ifC='P'  Then         beginRead (X,Y,V); Put (X,Y,V); Put (Y,X,-V);End        Else ifC='V'  Then  beginRead (x, y); Put (y,x,-1);End; ifI<m ThenReadln; End; ifSpfa ThenWriteln ('Reliable')ElseWriteln ('unreliable'); N:=0; m:=0;   READLN (N,M); End;End.

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POJ 2983:is The information Reliable? (differential constraint)