【LOJ#3097】[SNOI2019]通信（费用流）

题面

LOJ

题解

暴力就直接连\(O(n^2)\)条边。
然后分治/主席树优化连边就行了。
抄zsy代码，zsy代码是真的短

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
#define ll long long
#define MAX 50000
const int inf=1e9;
inline int read()
{int x=0;bool t=false;char ch=getchar();while((ch<'0'||ch>'9')&&ch!='-')ch=getchar();if(ch=='-')t=true,ch=getchar();while(ch<='9'&&ch>='0')x=x*10+ch-48,ch=getchar();return t?-x:x;
}
struct Line{int v,next,w,fy;}e[1000000];
int h[MAX],cnt=2;
inline void Add(int u,int v,int w,int fy)
{e[cnt]=(Line){v,h[u],w,fy};h[u]=cnt++;e[cnt]=(Line){u,h[v],0,-fy};h[v]=cnt++;
}
int S=0,T=0,tot;
ll dis[MAX],vis[MAX],TIM;
bool Update()
{ll mn=1e18;for(int u=0;u<=tot;++u)if(vis[u]==TIM)for(int i=h[u];i;i=e[i].next)if(e[i].w&&vis[e[i].v]!=TIM)mn=min(mn,dis[e[i].v]+e[i].fy-dis[u]);if(mn>=inf)return false;for(int u=0;u<=tot;++u)if(vis[u]==TIM)dis[u]+=mn;return true;
}
ll Flow,Cost;
int dfs(int u,int flow)
{if(u==T||!flow){Flow+=flow;Cost+=dis[S]*flow;return flow;}int ret=0;vis[u]=TIM;for(int i=h[u];i;i=e[i].next){int v=e[i].v;if(vis[v]!=TIM&&e[i].w&&dis[v]==dis[u]-e[i].fy){int d=dfs(v,min(flow,e[i].w));flow-=d;ret+=d;e[i].w-=d;e[i^1].w+=d;if(!flow)break;}}return ret;
}
void ZKW()
{dodo++TIM;while(dfs(S,inf));while(Update());
}
int n,W,a[MAX];
int p[MAX];
void Link(int l,int r)
{if(l==r)return;int mid=(l+r)>>1;Link(l,mid);Link(mid+1,r);int t=0;for(int i=l;i<=r;++i)p[++t]=a[i];sort(&p[1],&p[t+1]);t=unique(&p[1],&p[t+1])-p-1;for(int i=1;i<t;++i){Add(tot+i,tot+i+1,inf,p[i+1]-p[i]);Add(tot+i+1,tot+i,inf,p[i+1]-p[i]);}for(int i=l;i<=r;++i){int q=lower_bound(&p[1],&p[t+1],a[i])-p;if(i<=mid)Add(tot+q,i+n,1,0);else Add(i,tot+q,1,0);}tot+=t;
}
int main()
{n=read();W=read();for(int i=1;i<=n;++i)a[i]=read();S=n+n+1;T=n+n+2;tot=n+n+2;for(int i=1;i<=n;++i)Add(S,i,1,0),Add(i,T,1,W),Add(i+n,T,1,0);Link(1,n);ZKW();printf("%lld\n",Cost);return 0;
}