Value sequence (subsequence contribution problem)

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

#define rep(i,l,r) for(int i=(l);i<=(r);i++)
#define per(i,l,r) for(int i=(l);i>=(r);i--)
#define ll long long
#define pii pair<int, int>
#define mset(s,t) memset(s,t,sizeof(t))
#define mcpy(s,t) memcpy(s,t,sizeof(t))
#define fir first
#define pb push_back
#define sec second
#define sortall(x) sort((x).begin(),(x).end())
inline int read () {
	int x = 0, f = 0;
	char ch = getchar();
	while (!isdigit(ch)) f |= (ch=='-'),ch= getchar();
	while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
	return f?-x:x;
}
template<typename T> void print(T x) {
	if (x < 0) putchar('-'), x = -x;
	if (x >= 10) print(x/10);
	putchar(x % 10 + '0');
}
const int N = 1e6 + 10;
const int mod = 998244353;
int n;
ll a[N];

ll qmi (ll a, ll b, ll c ){
	ll ans = 1;
	while (b) {
		if (b & 1) ans =ans * a %c;
		b >>= 1;
		a = a * a % mod;
	}
	return ans;
}
void solve() {
   cin >> n;
   for (int i = 1; i<= n ;i++) {
   		cin >> a[i];
   }
   //sort(a + 1, a + 1 + n);
   ll ans = 1;
   a[n + 1] = 2e18;
   a[0] = 2e18;
   for (int i = 1, j = 1; i <= n ; i ++)  {
   		while (j < n && a[j + 1] == a[i]) {
   			j ++;	
		}
		
	
	    int len = j - i + 1;
	    
		if (((a[i - 1] < a[i] && a[j] < a[j + 1]) || (a[i - 1] > a[i] && a[j] > a[j + 1])) && ( i !=1 && j != n))
			ans = (ans * qmi(2, j - i + 1, mod) %mod) %mod;
		else {
			ans = ((ans * ((qmi(2, j - i + 1, mod) - 1) %mod + mod) %mod) %mod + mod) %mod;
		}
		j ++;
		i = j -1;
   }
   
   cout << ans  << endl;
}
int main () {
    int t;
    cin >> t;
    while (t --) solve();
    return 0;
}

https://ac.nowcoder.com/acm/contest/23481/B The first question is which numbers will not have no impact on the contribution If n <= 2 Then delete any one of them, either unchanged or reduced , Therefore, we can guess that deleting a number in the sequence must not increase For one of the positions , There are four size relationships , It can be found that the contribution will not change after the order of increasing or decreasing is deleted , Otherwise, it must be reduced , So one must be left .