bzoj 3931: [CQOI2015]网络吞吐量

这题考语文2333

其实是源点到汇点的流量一定要延最短路，可以有多条，求最大流。

要开long long。

code：

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#define pa pair<int,int>
#define LL long long
using namespace std;
const LL inf=(1LL<<40);
struct node{
int x,y,next,other;
LL c;
}b[200010],a[2110000];
int last[2010],h[2010],s[2010],st,ed,len=0;
int n,m;
LL v[510];
bool u[510];
void ins1(int x,int y,LL c)
{
b[++len].x=x;b[len].y=y;b[len].c=c;
b[len].next=last[x];last[x]=len;
}
void ins(int x,int y,LL c)
{
int k1=++len;
a[len].x=x;a[len].y=y;a[len].c=c;
a[len].next=last[x];last[x]=len;
int k2=++len;
a[len].x=y;a[len].y=x;a[len].c=0;
a[len].next=last[y];last[y]=len;
a[k1].other=k2;a[k2].other=k1;
}
bool bt_h()
{
memset(h,0,sizeof(h));
int l=1,r=2;s[l]=st;h[st]=1;
while(l!=r)
{
int x=s[l];
for(int i=last[x];i;i=a[i].next)
{
int y=a[i].y;
if(h[y]==0&&a[i].c>0) h[y]=h[x]+1,s[r++]=y;
}
l++;
}
return h[ed]!=0;
}
LL findflow(int x,LL f)
{
if(x==ed) return f;
LL t,ans=0;
for(int i=last[x];i;i=a[i].next)
{
int y=a[i].y;
if(h[x]+1==h[y]&&a[i].c>0&&ans<f)
{
ans+=(t=findflow(y,min(a[i].c,f-ans)));
a[i].c-=t;a[a[i].other].c+=t;
}
}
if(ans==0) h[x]=0;
return ans;
}
void dijkstra()
{
priority_queue<pa,vector<pa>,greater<pa> >q;
memset(v,127,sizeof(v));v[st]=0LL;
memset(u,false,sizeof(u));
q.push(make_pair(0,1));
while(!q.empty())
{
int x=q.top().second;q.pop();
if(u[x]) continue;
u[x]=true;
for(int i=last[x];i;i=b[i].next)
{
int y=b[i].y;
if(v[y]>v[x]+b[i].c)
{
v[y]=v[x]+b[i].c;
q.push(make_pair(v[y],y));
}
}
}
}
int main()
{
scanf("%d %d",&n,&m);
for(int i=1;i<=m;i++)
{
int x,y;LL c;scanf("%d %d %lld",&x,&y,&c);
ins1(x,y,c);ins1(y,x,c);
}
st=1;ed=n;dijkstra();
int tot=len;
memset(last,0,sizeof(last));len=0;
for(int i=1;i<=n;i++)
{
LL x;scanf("%lld",&x);
if(i==1||i==n) x=inf;
ins(i,i+n,x);
}
for(int i=1;i<=tot;i++)
if(v[b[i].x]+b[i].c==v[b[i].y])
ins(b[i].x+n,b[i].y,inf);
LL ans=0;st=1;ed=2*n;
while(bt_h()){ans+=findflow(st,inf);}
printf("%lld",ans);
}