洛谷P2766 最长不下降子序列问题 网络流_DP

Code:

#include<cstdio>

#include<iostream>

#include<vector>

#include<algorithm>

#include<queue>

#include<cstring>

using namespace std;

const int INF=1000000;

const int maxn=600;

# define  pb push_back

int A[maxn],f[maxn];

int s,t;

int ans=0;

struct Edge{

	int from,to,cap;

	Edge(int u,int v,int c):from(u),to(v),cap(c) {}

};

struct Dicnic{

   vector<Edge>edges;

   vector<int>G[maxn];

   int d[maxn],vis[maxn],cur[maxn];

   queue<int>Q;

   void addedge(int u,int v,int c){

   	edges.pb(Edge(u,v,c));               //正向弧

   	edges.pb(Edge(v,u,0));               //反向弧

   	int m=edges.size();

   	G[u].pb(m-2);

   	G[v].pb(m-1);

   }

   int BFS()

   {

    memset(vis,0,sizeof(vis));

    d[s]=0,vis[s]=1;Q.push(s);

    while(!Q.empty()){

    	int u=Q.front();Q.pop();

    	int sz=G[u].size();

    	for(int i=0;i<sz;++i){

    		Edge e=edges[G[u][i]];

    		if(!vis[e.to]&&e.cap>0){

    			d[e.to]=d[u]+1,vis[e.to]=1;

    			Q.push(e.to);

    		}

    	}

    }

    return vis[t];

   }

   int dfs(int x,int a){

       if(x==t)return a;

       int sz=G[x].size();

       int f,flow=0;

       for(int i=cur[x];i<sz;++i){

       	Edge e=edges[G[x][i]];

        cur[x]=i;

       	if(d[e.to]==d[x]+1&&e.cap>0){

       		f=dfs(e.to,min(a,e.cap));

       		if(f)

       		{

       			int u=G[x][i];

       			a-=f;

                edges[u].cap-=f;

                edges[u^1].cap+=f;

                flow+=f;

                if(a==0)break;

       		}

       	}

       }

       return flow;

   }

   int maxflow(){

   	while(BFS()){

      memset(cur,0,sizeof(cur));

      ans+=dfs(s,INF);

   	}

   	return ans;

   }

}op;

int main()

{

    int n;cin>>n;

    for(int i=1;i<=n;++i)cin>>A[i];

    f[1]=1;

    int anss=1;

    for(int i=2;i<=n;++i){

    	f[i]=1;

    	for(int j=1;j<i;++j)

    		if(A[j]<=A[i]){f[i]=max(f[i],f[j]+1);anss=max(anss,f[i]);}

    }

    s=0,t=510;

    for(int i=1;i<=n;++i){

    	if(f[i]==1)op.addedge(s,i,1);

    	if(f[i]==anss)op.addedge(i,t,1);

    }

    for(int i=1;i<n;++i)

    	for(int j=i+1;j<=n;++j)if(f[j]==f[i]+1&&A[j]>=A[i])op.addedge(i,j,1);

    cout<<anss<<endl;

    cout<<op.maxflow()<<endl;

    if(anss==1){cout<<n<<endl;return 0;}

    if(f[1]==anss)op.addedge(1,t,INF);

    if(f[n]==anss)op.addedge(n,t,INF);    //出边

    op.addedge(s,1,INF);

    if(f[n]==1)op.addedge(s,n,INF);        //入边

    for(int i=2;i<=n;++i)

    {

    	if(A[i]>=A[1]&&f[i]==f[1]+1)op.addedge(1,i,INF);

    }

    int fin=op.maxflow();

    if(fin>=INF)

    {

    	int t=fin/INF;

    	fin=(fin+t)%INF;

    }

    cout<<fin;

    return 0;

}