[网络流24题]最长递增子序列问题

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
inline int read()
{
    int x;char c;
    while((c=getchar())<‘0‘||c>‘9‘);
    for(x=c-‘0‘;(c=getchar())>=‘0‘&&c<=‘9‘;)x=(x<<3)+(x<<1)+c-‘0‘;
    return x;
}
#define MN 1000
#define MV 2000
#define ME 1000000
#define S MV+1
#define T MV+2
#define INF 0x7FFFFFFF
struct edge{int nx,t,w;}e[ME*2+5];
int n,h[MV+5],en=1,a[MN+5],f[MN+5],mx,d[MV+5],q[MV+5],qn,c[MV+5];
inline void ins(int x,int y,int w)
{
    e[++en]=(edge){h[x],y,w};h[x]=en;
    e[++en]=(edge){h[y],x,0};h[y]=en;
}
void build(int v)
{
    for(int i=1;i<=n;++i)
    {
        ins(i,i+n,(i>1&&i<n)||!v?1:INF);
        if(!f[i])ins(i+n,T,i==n&&v?INF:1);
        if(f[i]==mx)ins(S,i,i==1&&v?INF:1);
        for(int j=i;++j<=n;)if(a[i]<=a[j]&&f[i]==f[j]+1)ins(i+n,j,1);
    }
}
bool bfs()
{
    int i,j;
    memset(d,0,sizeof(d));
    for(d[q[i=qn=0]=S]=1;i<=qn;++i)for(j=c[q[i]]=h[q[i]];j;j=e[j].nx)
        if(e[j].w&&!d[e[j].t])d[q[++qn]=e[j].t]=d[q[i]]+1;
    return d[T];
}
int dfs(int x,int r)
{
    if(x==T)return r;
    int k,u=0;
    for(int&i=c[x];i;i=e[i].nx)if(e[i].w&&d[e[i].t]==d[x]+1)
    {
        k=dfs(e[i].t,min(r-u,e[i].w));
        u+=k;e[i].w-=k;e[i^1].w+=k;
        if(u==r)return u;
    }
    return d[x]=0,u;
}
int main()
{
    int i,j,ans=0;n=read();
    for(i=1;i<=n;++i)a[i]=read();
    for(i=n;--i;mx=max(mx,f[i]))for(j=n;j>i;--j)
        if(a[i]<=a[j])f[i]=max(f[i],f[j]+1);
    printf("%d\n",mx+1);
    for(build(0);bfs();)ans+=dfs(S,INF);
    printf("%d\n",ans);
    memset(h,ans=0,sizeof(h));build(en=1);
    while(bfs())ans+=dfs(S,INF);
    printf("%d",ans);
}