按题意直接模拟即可。

AC code：

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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    string s;
    cin >> s;
    int left = 0, right = s.size() - 1;
    while (left < right) {
        while (left < right && s[left] == ',') {
            left++;
        }
        while (left < right && s[right] == ',') {
            right--;
        }
        if (left < right && s[left] != s[right]) {
            cout << "No" << endl;
            return 0;
        }
        left++;
        right--;
    }
    cout << "Yes" << endl;
    return 0;
}

直接模拟即可。

#include <bits/stdc++.h>
using namespace std;
int a[4512], b[8912];
int main()
{
    int n, m, k;
    cin >> n >> m >> k;
    for (int i = 1; i <= n; i++)
    {
        int x;
        cin >> x;
        a[x]++;
    }
    for (int i = 1; i <= m; i++)
    {
        int s;
        cin >> s;
        while (s--)
        {
            int x;
            cin >> x;
            b[x] += a[i];
        }
    }
    int mp = 0, mi = 0;
    for (int i = 1; i <= k; i++)
        if (b[i] > mi) mi = b[i], mp = i;
    cout << mp << endl;
    return 0;
}