#include <bits/stdc++.h>
const int N=1e4+10;
using namespace std;
int n,ans,sum;
int a[N],b[N],f[N][N];
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
    	cin>>a[i];
	}
    for(int i=1;i<=n;i++){
    	cin>>b[i];
	}
    for(int i=1;i<=n;i++){
        sum=1;
        for(int j=1;j<=n;j++){
            f[i][j]=f[i-1][j];  
            if(a[i]==b[j]){
                f[i][j]=max(f[i][j],sum);
            }
            if(b[j]<a[i])  
                sum=max(sum,f[i][j]+1);            
        }
    }
    for(int i=1;i<=n;i++){
    	ans=max(ans,f[n][i]);
	}
    cout<<ans;
}

/************************************
Note Book:
************************************/
#include <iostream>
#include <cstdio>
#include <iomanip>
#include <cmath>
#include <algorithm>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
#include <math.h>
#define LL long long
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAXN = 5010;
int n , a[MAXN] , b[MAXN] , dp[MAXN] , maxn;
int main()
{
	cin >> n;
	for(int i = 1; i <= n; i++)
	{
		cin >> a[i];
	}
	for(int i = 1; i <= n; i++)
	{
		cin >> b[i];
	}
	for(int i = 1; i <= n; i++)
	{
		maxn = 0;
		for(int j = 1; j <= n; j++)
		{
			if(b[j] < a[i] && maxn < dp[j])
			{
				maxn = dp[j];
			}
			if(b[j] == a[i])
			{
				dp[j] = maxn + 1;
			}
		}
	}
	maxn = 0;
	for(int i = 1 ; i <= n ; i++ )
	{
		if(maxn < dp[i])
		{
			maxn = dp[i];
		}
	}
	cout << maxn;
	return 0;
}

我知道你们没题解活不了

#include <bits/stdc++.h>
using namespace std;
const int maxn=3e3+10;
int n,res;
int a[maxn],b[maxn];
int f[maxn][maxn];
int maxv;
int main()
{
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i];
    for(int i=1;i<=n;i++) cin>>b[i];
    for(int i=1;i<=n;i++) 
    {
        maxv=1;
        for(int j=1;j<=n;j++)
        {
            f[i][j]=f[i-1][j];  
            if(a[i]==b[j])
            {
                f[i][j]=max(f[i][j],maxv);
            }
            if(b[j]<a[i])  
                maxv=max(maxv,f[i][j]+1);            
        }
    }
    int res=0;
    for(int i=1;i<=n;i++) res=max(res,f[n][i]); 
    cout<<res<<endl;
    return 0;
}