OJ-Problems-Source/HDOJ/3157_autoAC.cpp

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#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<queue>
#define inf 0x7fffffff
using namespace std;
const int maxn=600;
const int M = 100000+10;
struct Edge
{
int to,cap,next;
}edge[M*2];
int head[maxn],edgenum;
int n,m,from,to,vnum,s,t;
void add(int u,int v,int cap)
{
edge[edgenum].to=v;
edge[edgenum].cap=cap;
edge[edgenum].next=head[u];
head[u]=edgenum++;
edge[edgenum].to=u;
edge[edgenum].cap=0;
edge[edgenum].next=head[v];
head[v]=edgenum++;
}
int level[maxn];
int gap[maxn];
void bfs(int to)
{
memset(level,-1,sizeof(level));
memset(gap,0,sizeof(gap));
level[to]=0;
gap[level[to] ]++;
queue<int> Q;
Q.push(to);
while (!Q.empty())
{
int u=Q.front() ;Q.pop() ;
for (int i=head[u] ;i!=-1 ;i=edge[i].next)
{
int v=edge[i].to;
if (level[v] != -1) continue;
level[v]=level[u]+1;
gap[level[v] ]++;
Q.push(v);
}
}
}
int cur[maxn];
int pre[maxn];
int SAP(int from,int to)
{
bfs(to);
memset(pre,-1,sizeof(pre));
memcpy(cur,head,sizeof(head));
int u=pre[from]=from,flow=0,aug=inf;
gap[from]=vnum;
while (level[from]<vnum)
{
bool flag=false;
for (int &i=cur[u] ;i!=-1 ;i=edge[i].next)
{
int v=edge[i].to;
if (edge[i].cap && level[u]==level[v]+1)
{
flag=true;
aug=min(aug,edge[i].cap);
pre[v]=u;
u=v;
if (v==to)
{
flow += aug;
for (u=pre[u] ;v!=from ;v=u ,u=pre[u])
{
edge[cur[u] ].cap -= aug;
edge[cur[u]^1 ].cap += aug;
}
aug=inf;
}
break;
}
}
if (flag) continue;
int minlevel=vnum;
for (int i=head[u] ;i!=-1 ;i=edge[i].next)
{
int v=edge[i].to;
if (edge[i].cap && level[v]<minlevel)
{
minlevel=level[v];
cur[u]=i;
}
}
if (--gap[level[u] ]==0) break;
level[u]=minlevel+1;
gap[level[u] ]++;
u=pre[u];
}
return flow;
}
int main()
{
while (scanf("%d%d",&n,&m)!=EOF)
{
if (!n && !m) break;
memset(head,-1,sizeof(head));
edgenum=0;
char c[5],c2[5];
int u,v;
int cap,f=M;
s=0 ;t=n+1 ;from=t+1 ;to=from+1 ;
vnum=to+1;
int sum=0;
for (int i=0 ;i<m ;i++)
{
scanf("%s%s%d",&c,&c2,&cap);
sum += cap;
if (c[0]=='+') u=s;
else sscanf(c,"%d",&u);
if (c2[0]=='-') v=t;
else sscanf(c2,"%d",&v);
add(u,v,f-cap);
add(from,v,cap);
add(u,to,cap);
}
int Maxflow=SAP(from,to);
int d=edgenum;
add(t,s,inf);
Maxflow += SAP(from,to);
int flag=0;
for (int i=head[from] ;i!=-1 ;i=edge[i].next)
{
if (edge[i].cap) {flag=1;break; }
}
if (Maxflow==sum) printf("%d\n",edge[(d^1)].cap);
else printf("impossible\n");
}
return 0;
}