#include<bits/stdc++.h>
#define MAX_N 100010
using namespace std;
int dp[MAX_N];
int a[MAX_N], b[MAX_N];
int now = 0;
int bound(int x)
{
	int L = 1, R = now;
	while (L < R)
	{
		int mid = (L + R) >> 1;
		if (b[dp[mid]] > b[x])
			R = mid;
		else
			L = mid + 1;
	}
	return L;
}
int main()
{
	int n;
	int temp;
	cin >> n;
	for (int i = 1; i <= n; i++)
		cin >> a[i];
	for (int i = 1; i <= n; i++)
	{
		cin >> temp;
		b[temp] = i;
	}
	for (int i = 1; i <= n; i++)
		{
		if (b[a[i]] > b[dp[now]])
			dp[++now] = a[i];
		else
			dp[*lower_bound(dp+1,dp+now,a[i])] = a[i];
		}
	cout << now;
}

看到题解有个用二分（上面有大佬写的bound函数），但为什么我差不多的思路，用的是lower_bound就只有20，感谢