WA*2求条

#include<bits/stdc++.h>
#define ll long long
#define ull unsigned ll
#define lll __int128
#define db double
#define ldb long db
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define	pll pair<ll, ll>
#define endl '\n'
#define ft first
#define sd second
using namespace std;
int n;
int a[200005];
bool check(int x) {
	stack<pii> stk;
	for(int i = 2; i <= n; i++) {
		if(a[i] > a[i - 1]) {
			continue;
		}
		while(!stk.empty() && stk.top().ft > a[i]) {
			stk.pop();
		}
		if(stk.empty() || stk.top().ft != a[i]) {
			stk.push({a[i], 2});
		} else {
			int lst = a[i] + 1;
			while(!stk.empty() && stk.top().ft == lst - 1 && stk.top().sd == x) {
				lst--;
				stk.pop();
			}
			if(stk.empty()) {
				return 0;
			}
			if(stk.top().ft != lst - 1) {
				stk.push({lst - 1, 2});
			} else {
				stk.top().sd++;
			}
		}
	}
	return 1;
}
int main() {
	//freopen(".in", "r", stdin);
	//freopen(".out", "w", stdout);
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin >> n;
	bool f = 1;
	for(int i = 1; i <= n; i++) {
		cin >> a[i];
		f &= (a[i] > a[i - 1]);
	}
	if(f) {
		cout << 1 << endl;
		return 0;
	}
	int l = 2, r = n;
	int ans;
	while(l <= r) {
		int mid = (l + r) / 2;
		if(check(mid)) {
			ans = mid;
			r = mid - 1;
		} else {
			l = mid + 1;
		}
	}
	cout << ans << endl;
	return 0;
}

/*
Progress is impossible without change, and those who cannot change their minds cannot change anything.
NEVER GIVE UP.
*/