[二分答案 上下界费用流验证] 计蒜客 91 地铁 & HDU 5263 平衡大师

#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cstring>
#define cl(x) memset(x,0,sizeof(x))
using namespace std;

inline char nc(){
static char buf[100000],*p1=buf,*p2=buf;
if (p1==p2) { p2=(p1=buf)+fread(buf,1,100000,stdin); if (p1==p2) return EOF; }
return *p1++;
}
inline void read(int &x){
char c=nc(),b=1;
for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;
for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;
}

const int N=105;
const int M=100005;

#define V G[p].v
struct edge{
int u,v,f,w;
int next;
}G[M];
int head
,inum=1;

inline void add(int u,int v,int w,int f,int p){
G[p].u=u; G[p].v=v; G[p].w=w; G[p].f=f; G[p].next=head[u]; head[u]=p;
}
inline void link(int u,int v,int w,int f){
add(u,v,w,f,++inum); add(v,u,-w,0,++inum);
}
inline void clear(){
cl(head); inum=1;
}

int S,T;
int pre
,dis
,ins
;
int Q[1000005],l,r;

#define V G[p].v
int Mincost;
inline bool SPFA(){
for (int i=1;i<=T;i++) dis[i]=1<<30,pre[i]=0,ins[i]=0;
l=r=-1; dis[S]=0; Q[++r]=S; ins[S]=1;
while (l!=r){
int u=Q[++l]; ins[u]=0;
for (int p=head[u];p;p=G[p].next)
if (G[p].f && dis[V]>dis[u]+G[p].w){
dis[V]=dis[u]+G[p].w; pre[V]=p;
if (!ins[V]) Q[++r]=V,ins[V]=1;
}
}
if (dis[T]==(1<<30)) return 0;
int minv=1<<30;
for (int p=pre[T];p;p=pre[G[p].u])
minv=min(minv,G[p].f);
Mincost+=minv*dis[T];
for (int p=pre[T];p;p=pre[G[p].u])
G[p].f-=minv,G[p^1].f+=minv;
return 1;
}

int n,m,K;
int us[N*N],vs[N*N],ds
;
int s,t;

inline bool check(int v){
clear();
s=n+1; t=n+2; S=n+3; T=n+4;
link(t,s,0,1<<30);
for (int i=1;i<=m;i++) link(us[i],vs[i],1,1);
for (int i=1;i<=n;i++)
if (ds[i]>=v){
link(s,i,0,2*v);
link(S,i,0,ds[i]-v); link(s,T,0,ds[i]-v);
}else if (ds[i]<=-v){
link(i,t,0,2*v);
link(S,t,0,-ds[i]-v); link(i,T,0,-ds[i]-v);
}else{
link(s,i,0,ds[i]+v); link(i,t,0,v-ds[i]);
}
Mincost=0; while (SPFA());
return Mincost<=K;
}

int main(){
int Q,Case=0;
freopen("t.in","r",stdin);
freopen("t.out","w",stdout);
read(Q);
while (Q--){
read(n); read(m); read(K); K=m-K; cl(ds);
for (int i=1;i<=m;i++) read(us[i]),read(vs[i]),ds[vs[i]]--,ds[us[i]]++;
int L=-1,R=n,MID;
while (L+1<R)
if (check(MID=(L+R)>>1))
R=MID;
else
L=MID;
printf("Case %d: %d\n",++Case,R);
}
return 0;
}