67. B. Most socially-distanced subsequence (Code Forces - Round 649 - Div. 2).cpp

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int t;
    cin >> t;
    while(t--){
        int n;
        cin >> n;
        vector<int>a(n);
        for(int i=0; i<n; i++){
            cin >> a[i];
        }
        vector<int>ans;
        for(int i=0; i<n; i++){
            if(i==0 || i==n-1 || (a[i]>a[i-1] && a[i]>a[i+1])|| (a[i]<a[i-1] && a[i]<a[i+1]))
                ans.push_back(a[i]);
        }
        cout << ans.size() << "\n";
        for(auto i: ans)
            cout << i << " ";
    }
}