POJ 3255 dijkstra次短路

program p3255;

Type
rec=record
e,w,next:longint;
end;

Var
n,m,i,j,k,nowmin,minj,mink,u,top,st,ed,ww:longint;
y:rec;
a:array[0..200002] of rec;
b:array[0..10002] of longint;
v:array[1..2,0..10002] of boolean;
d:array[1..2,0..10002] of longint;

Procedure add(st,ed,ww:longint);inline;
begin
inc(top);
with a[top] do
begin
e:=ed;
w:=ww;
next:=b[st];
end;
b[st]:=top;
end;

begin
readln(n,m);
top:=0;
for i:=1 to m do
begin
readln(st,ed,ww);
add(st,ed,ww);
add(ed,st,ww);
end;
fillchar(v,sizeof(v),false);
fillchar(d,sizeof(d),$7f);
d[1,1]:=0;
for i:=1 to 2*n do
begin
nowmin:=maxlongint;
for j:=1 to n do
for k:=1 to 2 do
if not v[k,j] then
if d[k,j]<nowmin then
begin
nowmin:=d[k,j];
minj:=j;mink:=k;
end;

if nowmin=maxlongint then break;
v[mink,minj]:=true;
u:=b[minj];
while u<>0 do
begin
y:=a[u];
u:=y.next;
if nowmin+y.w<d[1,y.e] then
begin
d[2,y.e]:=d[1,y.e];
d[1,y.e]:=nowmin+y.w;
end else
if nowmin+y.w<d[2,y.e] then
d[2,y.e]:=nowmin+y.w;
end;
end;
writeln(d[2,n]);
readln;
end.