最长不下降子序列问题

#include<queue>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define N 1050
const int inf = 0x3f3f3f3f;
inline int rd()
{
    int f=1,c=0;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){c=10*c+ch-‘0‘;ch=getchar();}
    return f*c;
}
int n,m,S,T,hed[N],cnt=-1,a[N];
struct EG
{
    int to,nxt,w,c;
}e[4*N*N];
void ae(int f,int t,int w,int c)
{
    e[++cnt].to = t;
    e[cnt].nxt = hed[f];
    e[cnt].w = w;
    e[cnt].c = c;
    hed[f] = cnt;
}
void AE(int f,int t,int w,int c)
{
    ae(f,t,w,c);
    ae(t,f,0,-c);
}
int dep[N],fl[N];
int pre[N],fa[N];
bool vis[N];
queue<int>q;
bool spfa()
{
    memset(dep,0x3f,sizeof(dep));
    dep[S]=0,fl[S]=inf,vis[S]=1;q.push(S);
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        for(int j=hed[u];~j;j=e[j].nxt)
        {
            int to = e[j].to;
            if(e[j].w&&dep[to]>dep[u]+e[j].c)
            {
                dep[to] = dep[u]+e[j].c;
                fl[to] = min(fl[u],e[j].w);
                pre[to] = j,fa[to] = u;
                if(!vis[to])
                {
                    vis[to] = 1;
                    q.push(to);
                }
            }
        }
        vis[u] = 0;
    }
    return dep[T] != inf;
}
void mcmf(bool typ)
{
    int ct = 0;
    bool fd = 0;
    while(spfa())
    {
        if(!fd)m = fl[T]*dep[T],fd=1;
        if(fl[T]*dep[T]==m)ct++;
        else break;
        int u = T;
        while(u!=S)
        {
            e[pre[u]].w-=fl[T];
            e[pre[u]^1].w+=fl[T];
            u = fa[u];
        }
    }
    if(!typ)
    {
        printf("%d\n%d\n",-m,ct);
    }else
    {
        printf("%d\n",ct);
    }
}
void sol1()
{
    memset(hed,-1,sizeof(hed));
    for(int i=1;i<=n;i++)
    {
        AE(S,i<<1,1,-1);
        AE(i<<1|1,T,1,0);
        AE(i<<1,i<<1|1,1,0);
    }
    for(int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++)
            if(a[j]>=a[i])
                AE(i<<1|1,j<<1,1,-1);
    mcmf(0);
}
void sol2()
{
    memset(hed,-1,sizeof(hed));
    for(int i=2;i<n;i++)
    {
        AE(S,i<<1,1,-1);
        AE(i<<1|1,T,1,0);
        AE(i<<1,i<<1|1,1,0);
    }
    AE(S,2,inf,-1);
    AE(2,3,inf,0);
    AE(3,T,1,0);
    AE(S,n<<1,1,-1);
    AE(n<<1,n<<1|1,inf,0);
    AE(n<<1|1,T,inf,0);
    for(int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++)
            if(a[j]>=a[i])
                AE(i<<1|1,j<<1,1,-1);
    mcmf(1);
}
int main()
{
    n = rd();S = 0,T = 1;
    for(int i=1;i<=n;i++)a[i] = rd();
    sol1();
    sol2();
    return 0;
}