最長不XX子序列

#include <iostream>
#include <cstdio>
using namespace std;

int a[200020];
int g[200020];
int k;

void Find(int i)  //最長不下降子序列
{
    int l = 1, r = k;
    int ans = 0;
    while (l <= r)
    {
        int mid = (l+r) >> 1;
        if (g[mid] <= a[i])
        {
            ans = mid;
            l = mid+1;
        }
        else
            r = mid-1;
    }

    if (g[ans+1] > a[i] || g[ans+1] == 0)
        g[ans+1] = a[i];
    if (ans == k)
        k++;
}

void Find_(int i)  //最長不上升子序列
{
    int l = 1, r = k;
    int ans = 0;
    while (l <= r)
    {
        int mid = (l+r) >> 1;
        if (g[mid] >= a[i])
        {
            ans = mid;
            l = mid+1;
        }
        else
            r = mid-1;
    }

    if (g[ans+1] < a[i] || g[ans+1] == 0)
        g[ans+1] = a[i];
    if (ans == k)
        k++;
}

int main()
{
	int n;
	
	cin >> n;
	for (int i=1; i<=n; i++) cin >> a[i];
	
	g[1] = a[1]; k = 1;
	for (int i=2; i<=n; i++) Find(i);
	cout << "最長不下降子序列的的長度是：" << k << endl;
	
	for (int i=0; i<=n; i++) g[i] = 0;
	g[1] = a[1]; k = 1;
	for (int i=2; i<=n; i++) Find_(i);
	cout << "最長不上升子序列的長度是：" << k << endl;
	
	return 0;
}