A - DZY Loves Sequences

Posted 2021-11-05 thusloop

DZY Loves Sequences
b[i] 为 i 开始上升序列的右边界。

//#pragma GCC optimize(2)
//#pragma GCC optimize(3,"Ofast","inline")
#include<bits/stdc++.h>
#define int long long
#define fi first
#define se second
#define pb push_back
#define pii pair<int,int>
#define ios ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
using namespace std;
const int inf=2e18+100;
const int maxn=2e5+100;
int a[maxn],b[maxn];
signed main()
{
	IOS
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i]; 
	}
	if(n==1)
	{
		cout<<"1\\n";
		return 0;
	}
	if(n==2)
	{
		cout<<"2\\n";
		return 0;
	}
	int l=1,r=1;
	while(r<=n)
	{
		if(l>=r)r=l+1;
		while(r<=n&&a[r]>a[r-1])
		{
			r++;
		}
		b[l]=r-1;
		l++;
		//if(l>r)r=l+1;
	}
	for(int i=l;i<r;i++)b[i]=n;
	int ans=1;
	for(int i=1;i<=n;i++)
	{
		int l1=i,r1=b[i];
		int l2=b[i]+1,r2=b[b[i]+1];
		ans=max(ans,r1-l1+1);
		if(l2>n)continue;
		ans=max(ans,r2-l2+1);
		if(r1-l1+1>1)
		{
			if(a[l2]-1>a[r1-1])ans=max(ans,r2-l1+1);
			if(r2-l2+1>=1)ans=max(ans,r1-l1+2);
		}
		else if(r2-l2+1>=1)
		{
			ans=max(ans,r2-l2+2);
		}
		if(r2-l2+1>1)
		{
			if(a[l2+1]-1>a[r1])ans=max(ans,r2-l1+1);
			if(r1-l1+1>=1)ans=max(ans,r2-l2+2);
		}
		else if(r1-l1+1>=1)
		{
			ans=max(ans,r1-l1+2);
		}
	}
	cout<<ans<<"\\n";
}