ZOJ-2676-Network Wars（01分数规划+最小割）

链接：http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=1676







while(  ( t=DFS(S,T,INF) ) >=eps)没加括弧wa到哭

//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <queue>
#include <cmath>
#include <string>
#include <map>
#include <stack>
using namespace std;
#define INF 0x3f3f3f3f
#define MAXN 5007
#define MAXM 5007
int n,m;
const int mod=499999;
#define eps 1e-9
int x[MAXN],y[MAXN],used[MAXN],vis[MAXN];
double z[MAXN];
int GAP[MAXN],dis[MAXN];
int deep[MAXN];
struct node
{
int v,next;
double flow;
} edge[MAXM];
int ind, head[MAXN];
void add_(int u, int v, double flow)
{
edge[ind].v=v;
edge[ind].flow=flow;
edge[ind].next=head[u];
head[u]=ind++;
edge[ind].v=u;
edge[ind].flow=0;
edge[ind].next=head[v];
head[v]=ind++;
}
bool BFS(int S, int T)
{
memset(deep,0,sizeof(deep));
deep[S]=1;
queue<int> q;
q.push(S);
while(!q.empty())
{
int u=q.front();
q.pop();
for(int i=head[u]; i+1; i=edge[i].next)
{
int v= edge[i].v;
if(!deep[v]&&edge[i].flow>=eps)
{
deep[v]=deep[u]+1;
q.push(v);
if(v==T)return 1;
}
}
}
return 0;
}
double DFS(int S, int T, double max_)
{
if(S==T)return max_;
double ans=0,f;
for(int i=head[S]; i+1; i=edge[i].next)
{
int v=edge[i].v;
if(deep[S]+1==deep[v] && edge[i].flow>eps)
{
f=DFS(v,T,min(max_-ans,edge[i].flow));
ans+=f;
edge[i].flow-=f;
edge[i^1].flow+=f;
}
}
if(eps<=ans)return ans;
deep[S]=0;
return 0;
}
double Dinic(int S, int T)
{
double ans=0,t;
while(BFS(S,T))
{
while( ( t=DFS(S,T,INF) ) >=eps)
ans+=t;
}
return ans;
}
void D(int u)
{
vis[u]=1;
for(int i=head[u]; i+1; i=edge[i].next)
{
int v=edge[i].v;
if(!vis[v] && edge[i].flow>=eps)D(v);
}
}
int main()
{
int cp=0;
while(scanf("%d%d",&n,&m)!=EOF)
{
for(int i=0; i<m; ++i)
scanf("%d%d%lf",&x[i],&y[i],&z[i]);
double l=0.0,r=0.0,ans,mid;
for(int i=0; i<m; ++i)r+=z[i];
int cnt=0;
while(r-l>=eps)
{
mid=(l+r)/2.0;
ind=0;
ans=0;
memset(head,-1,sizeof(head));
for(int i=0; i<m; ++i)
{
if(z[i]<mid)
ans+=z[i]-mid;
else
{
add_(x[i],y[i],z[i]-mid);
add_(y[i],x[i],z[i]-mid);
}
}
ans+=Dinic(1,n);
if(fabs(ans)<eps)break;
if(ans<0)r=mid;
else l=mid;
}
memset(used,0,sizeof(used));
for(int i=0; i<m; ++i)if(z[i]<mid)used[i]=1;
memset(vis,0,sizeof(vis));
D(1);
for(int i=0; i<m; ++i)
if(vis[ x[i] ]!=vis[ y[i] ] || used[i])
cnt++;
printf("%d\n",cnt);
for(int i=0; i<m; ++i)
if(vis[ x[i] ]!=vis[ y[i] ] || used[i])
{
cnt--;
if(cnt)
printf("%d ",i+1);
else printf("%d\n",i+1);
}
printf("\n");
}
return 0;
}

/*
6 8
1 2 3
1 3 3
2 4 2
2 5 2
3 4 2
3 5 2
5 6 3
4 6 3
4 5
1 2 2
1 3 2
2 3 1
2 4 2
3 4 2

*/