POJ2455 Secret Milking Machine ——二分答案+网络流——Pku2455

Program Secret;//By_Poetshy
Const
maxn=40000;
Var
i,j,k,m,n,p,t,d         :Longint;
pre,other,last,data     :Array[1..maxn*2]of Longint;
a,b                     :Array[1..200]of Longint;
v                       :Array[1..200]of Boolean;
f,c                     :Array[1..200,1..200]of Longint;
l,r,mid,ans,max         :Longint;

Function Min(i,j:Longint):Longint;
begin
if i<j then exit(i);exit(j);
end;

Function Check(i:Longint):Boolean;
var j,k,p,q,sum,head,tail   :Longint;
seq                     :Array[1..maxn]of Longint;
begin
fillchar(f,sizeof(f),0);
fillchar(c,sizeof(c),0);
for p:=1 to n do
begin
j:=last[p];
while j<>0 do
begin
k:=other[j];
if data[j]<=i then inc(c[p,other[j]]);
j:=pre[j];
end;
end;
repeat
fillchar(v,sizeof(v),0);
head:=0;tail:=1;seq[1]:=1;
a[1]:=0;b[1]:=maxlongint;
v[1]:=true;
while head<tail do
begin
inc(head);p:=seq[head];
for q:=1 to n do
if (c[p,q]<>0)and(f[p,q]<c[p,q])and(not v[q])then
begin
v[q]:=true;
a[q]:=p;b[q]:=Min(c[p,q]-f[p,q],b[p]);
inc(tail);seq[tail]:=q;
end;
if seq[tail]=n then break;
end;
if v
then
begin
p:=n;
while p<>0 do
begin
if a[p]<>0 then inc(f[a[p],p],b
);
p:=a[p];
end;
end;
until not v
;
sum:=0;
for p:=1 to n-1 do inc(sum,f[p,n]);
if sum>=t then exit(true);
exit(false);
end;

BEGIN
readln(n,p,t);
for i:=1 to p do
begin
readln(m,j,d);
inc(k);pre[k]:=last[m];last[m]:=k;other[k]:=j;data[k]:=d;
inc(k);pre[k]:=last[j];last[j]:=k;other[k]:=m;data[k]:=d;
if d>max then max:=d;
end;
l:=0;r:=max;
while l<=r do
begin
mid:=(l+r)>>1;
if check(mid) then
begin
ans:=mid;
r:=mid-1;
end else l:=mid+1;
end;
writeln(ans);
END.