Educational Codeforces Round 118 (Rated for Div. 2) D. MEX Sequences

f[x][0/1]为最大值为x的合法序列个数,
f[x][0]:包含0~x, f[x][1]:包含0~x-2和x

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

#define fr first
#define se second
#define et0 exit(0);
#define rep(i, a, b) for(int i = (a); i <= (b); i ++)
#define rrep(i, a, b) for(int i = (a); i >= (b); i --)

typedef long long LL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef unsigned long long ULL;

const int INF = 0X3f3f3f3f, N = 2e6 + 10, MOD = 998244353;
const double eps = 1e-7;

void work() {
	int n;
	cin >> n;
	vector<vector<LL>> f(n + 4, vector<LL>(2));
	// 最大值为x的合法序列个数, f[x][0]:包含0~x, f[x][1]:包含0~x-2和x
	f[0][0] = 1;
	rep(i, 1, n) {
		int x;
		cin >> x;
		x++;
		f[x][0] += f[x][0] + f[x - 1][0];
		f[x][1] += f[x][1];
		f[x + 2][1] += f[x + 2][1];
		if (x > 1) f[x][1] += f[x - 2][0];
		f[x][0] %= MOD, f[x][1] %= MOD, f[x + 2][1] %= MOD;
	}
	LL ans = 0;
	rep(i, 1, n + 1) ans += f[i][0] + f[i][1], ans %= MOD;
	cout << ans << endl;
}

signed main() {
	int test;
	cin >> test;

	while (test--) {
		work();
	}

	return 0;
}