Several implementations are possible; for example, the sample code in the end of this editorial performs the following procedure.

1. First, receive the input.

2. Inspect people \(i = 1, 2, \ldots, N\). Store the people betting on \(X\) into the variable-length array \(\mathrm{vec}\).

3. For each person \(i\) in \(\mathrm{vec}\), count how many bets person \(i\) made and store the number to \(c_i\). Find the minimum value \(C_{\min}\) among them.

4. For each person \(i\) in \(\mathrm{vec}\), check if \(C_i = C_{\min}\), i.e. if that person made the minimum bets; if so, store it to the variable-length array \(\mathrm{ans}\).

5. Print the size of \(\mathrm{ans}\) and its elements in ascending order.

The following is a sample code in C++ language.

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main(void)
{
    int n, x, c[101];
    vector<int> a[101];
    
    cin >> n;
    for(int i = 1; i <= n; i++){
    	cin >> c[i];
        a[i].resize(c[i]);
        for(int j = 0; j < c[i]; j++) cin >> a[i][j];
    }
    cin >> x;
    
    vector<int> vec;
    for(int i = 1; i <= n; i++){
        for(int j = 0; j < c[i]; j++) if(a[i][j] == x) vec.push_back(i);
    }
    
    int cmin = 37;
    for(auto i : vec) cmin = min(cmin, c[i]);
    
    vector<int> ans;
    for(auto i : vec) if(c[i] == cmin) ans.push_back(i);
    
    cout << ans.size() << endl;
    for(auto b : ans) cout << b << " ";
    cout << endl;
    
    return 0;
}