思路：反向推x可以由哪些等级的种子得到。

AC代码：

#include<vector>
#include<cstring>
using namespace std;
#define ll long long
#define PLL pair<ll,ll>
#define fi first
#define se second
const int Max = 1e5 + 5;
PLL tree[20];
int a[Max];

int main() {
    int n;
    ll x;
    cin >> n;
    int max_a = 0;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        if (a[i] > max_a)
            max_a = a[i];
    }
    cin >> x;
    tree[0].fi = x;
    tree[0].se = x;
    int layers = 1;
    while (tree[layers - 1].se < max_a) {
        tree[layers].se = tree[layers - 1].se * 3;
        tree[layers].fi = tree[layers - 1].fi * 3 - 2;
        layers++;
    }
    ll result[20];
    for (int i = 0; i < 20; i++)
        result[i] = 0;
    for (int i = 1; i <= n; i++) {
        int j = 0;
        while (a[i] > tree[j].se) {
            j++;
        }
        if (j == 0 && a[i] == x) {
            result[j]++;
        }
        else if (j > 0) {
            if (tree[j].fi <= a[i]) {
                result[j] += (1 << j);
            }
        }
    }
    ll ans = 0;
    for (int i = 0; i < layers; i++) {
        if (result[i] > ans)
            ans = result[i];
    }
    cout << ans;
    return 0;
}