```cpp
program cowescape;
var
m,i,j,aa,bb,x,y,t:longint;
a,b:array[1..5] of longint;
map:array[0..1000,0..1000] of longint;
procedure tr(xxx,yyy,time:longint);
var
aa,bb,k:longint;
begin
if map[xxx,yyy]=-1 then
begin
writeln(time);
halt;
end;
for k:=1 to 4 do
begin
aa:=xxx+a[k];
bb:=yyy+b[k];
if (aa<0) or (bb<0) then continue;
if (map[aa,bb]>time+1) or (map[aa,bb]=-1) then tr(aa,bb,time+1);
end;
end;
function min(xx,yy:longint):longint;
begin
if xx<yy then exit(xx) else exit(yy);
end;
begin
readln(m);
a[1]:=0;
a[2]:=1;
a[3]:=0;
a[4]:=-1;
a[5]:=0;
b[1]:=1;
b[2]:=0;
b[3]:=-1;
b[4]:=0;
b[5]:=0;
fillchar(map,sizeof(map),-1);
for i:=1 to m do
begin
readln(x,y,t);
for j:=1 to 5 do
begin
aa:=x+a[j];
bb:=y+b[j];
if (aa<0) or (bb<0) then continue;
if (map[aa,bb]<>-1) then map[aa,bb]:=min(map[aa,bb],t)
else map[aa,bb]:=t;
end;
end;
tr(0,0,0);
writeln(-1);
end.
```
by Hangben @ 2016-10-23 18:28:22
另：这题有什么优化剪枝？
by Hangben @ 2016-10-23 18:29:06