最长公共上升子序列 (LCIS)

DP优化经典
设 dp[i][j] 表示以 b[j] 结尾的 a[i] 以前的 LCIS 的长度

#include <iostream>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <cstdio>
#define inf 0x3f3f3f3f
using namespace std;
const int MAXN = 3005;
int n, dp[MAXN][MAXN], ans;
long long a[MAXN], b[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];
	}
	a[0] = b[0] = -inf;
	for(int i = 1; i <= n; i++) {
		int val = 0;
		for(int j = 1; j <= n; j++) {
			if(a[i] == b[j]) {
				dp[i][j] = val + 1;
			}else dp[i][j] = dp[i - 1][j];
			if(b[j] < a[i]) val = max(val, dp[i - 1][j]);
			ans = max(ans, dp[i][j]);
		}
	}
	cout << ans << endl;
	return 0;
}