不知道是不是数据的问题，但是我看到好多人都不是45，求调。
跟正解差得比较远，dp[i][j]表示a取i个b取j个最大长度，mmr[i][j]表示a取i个b取j个在长度最大时末尾数最小值，lmr[i][j]表示a取i个b取j个长度最大、末尾数最小时倒数第二个数的最小值

#include <bits/stdc++.h>
using namespace std;

int main()
{
	long long n;
    cin >> n;
	long long a[n + 5], b[n + 5];
	for (int i = 1; i <= n; i++)
		cin >> a[i];
	for (int i = 1; i <= n; i++)
		cin >> b[i];
	long long dp[n + 5][n + 5];
	long long mmr[n + 5][n + 5], lmr[n + 5][n + 5];
	memset(dp, 0, sizeof(dp));
	memset(mmr, 0, sizeof(mmr));
	memset(lmr, 0, sizeof(lmr));
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++)
		{		
			if (a[i] > mmr[i - 1][j - 1] && a[i] == b[j])
				dp[i][j] = dp[i - 1][j - 1] + 1,
				lmr[i][j] = mmr[i - 1][j - 1],
				mmr[i][j] = a[i];
			else if (a[i] < mmr[i - 1][j - 1] && a[i] > lmr[i - 1][j - 1] && a[i] == b[j])
				dp[i][j] = dp[i - 1][j - 1],
				lmr[i][j] = lmr[i - 1][j - 1],
				mmr[i][j] = a[i];
			else
				if (dp[i - 1][j] == dp[i][j - 1])
					if (mmr[i - 1][j] == mmr[i][j - 1])
						dp[i][j] = dp[i - 1][j],
						mmr[i][j] = mmr[i - 1][j],
						lmr[i][j] = min(lmr[i - 1][j], lmr[i][j - 1]);
					else if (mmr[i - 1][j] < mmr[i][j - 1])
						dp[i][j] = dp[i - 1][j],
						mmr[i][j] = mmr[i - 1][j],
						lmr[i][j] = lmr[i - 1][j];
					else
						dp[i][j] = dp[i][j - 1],
						mmr[i][j] = mmr[i][j - 1],
						lmr[i][j] = lmr[i][j - 1];
				else if (dp[i - 1][j] > dp[i][j - 1])
					dp[i][j] = dp[i - 1][j],
					mmr[i][j] = mmr[i - 1][j],
					lmr[i][j] = lmr[i - 1][j];
				else
					dp[i][j] = dp[i][j - 1],
					mmr[i][j] = mmr[i][j - 1],
					lmr[i][j] = lmr[i][j - 1];
	//		cout << i << " " << j << endl;
	//		cout << dp[i][j] << " " << mmr[i][j] << " " << lmr[i][j] << endl;
		}
	cout << dp[n][n] << endl;
	return 0;
}