P2766 最长不下降子序列问题

#include <iostream>
#include<cmath>
#include <queue>
#include <cstring>
using namespace std;
 const int N =2e6+2,M=5e4+100;
 
 
 int g[N],a[N],L;
  
 const int inf =1e9+7;
 
 int all=1,hd[N],go[M],w[M],nxt[M];
  
 int S,T,n,m;
 int dis[M],ans=0,now[M];
  
 void add_(int x,int y,int z){
     nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
     w[all]=z;
     swap(x,y);
     nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
     w[all]=0;
 }
  bool bfs(){
     for(int i=0;i<M;i++)dis[i]=inf;
     queue<int> q;
     q.push(S);
     now[S]=hd[S];
     dis[S]=0;
      
     while(q.empty()==0){
         int x=q.front();
         q.pop();
         for(int i=hd[x];i;i=nxt[i]){
             int y=go[i];
             if(w[i]>0&&dis[y]==inf){
                 dis[y]=dis[x]+1;
                 now[y]=hd[y];
                 q.push(y);
                 if(y==T) return 1;
             }
         }
     }
     return 0;
 }
 int dfs(int x,int sum){
     if(x==T) return sum;
     int k,res=0;
      
     for(int i=now[x];i&& sum ;i=nxt[i]){
         now[x]=i;
         int y=go[i];
         if(w[i]>0&&(dis[y]==dis[x]+1)){
             k=dfs(y,min(sum,w[i]));
             if(k==0) dis[y]=inf;
             w[i]-=k;
             w[i^1]+=k;
             res+=k;
             sum-=k;
         }
     }
     return res;
 }
  
  
 signed main(){
 	int i,j,k;
 	cin>>n;
 	for(i=1;i<=n;i++) cin>>a[i],g[i]=1;
 	
 	for(i=1;i<=n;i++)
 	 for(k=1;k<i;k++)
 	  if(a[i]>=a[k]) 
 	    g[i]=max(g[i],1+g[k]);
    for(i=1;i<=n;i++) L=max(L,g[i]);
 	if(L==1){
 		printf("1\n%d\n%d\n",n,n); return 0 ;
 	}
 	cout<<L<<endl;
 	S=0,T=2*n+1;
 	for(i=1;i<=n;++i) if(g[i]==1) add_(S,i,1) ;
 	for(i=1;i<=n;i++) if(g[i]==L) add_(i+n,T,1);
 	for(i=1;i<=n;++i) add_(i,i+n,1); 
 	
 	for(i=1;i<=n;i++)
 	 for(k=1;k<i;k++)
 	  if(g[i]==g[k]+1&&a[i]>=a[k]) add_(k+n,i,1);
 	int ans=0;
 	while(bfs()) ans+=dfs(S,inf) ;
 	cout<<ans<<endl;
 	
 	add_(1,1+n,inf); add_(S,1,inf);
 	if(g[n]==L) add_(n,2*n,inf),add_(2*n,T,inf);
 	
 	while(bfs()) ans+=dfs(S,inf) ;
 	cout<<ans<<endl;
 }