1862B - Sequence Game - CodeForces Solution

// Online C++ compiler to run C++ program online
#include<iostream>
#include<bits/stdc++.h>
#include<vector>
using namespace std;

vector<int> sequence(vector<int> b, int n){
    
    vector<int> ans;
    ans.push_back(b[0]);
    for(int i=1; i<b.size(); i++){
        
        if(b[i]<b[i-1] && (ans.size()<=2*n)){
            
                if(b[i]==1){
                    
                    ans.push_back(b[i]);
                }
                else{
                    
                    ans.push_back(b[i]-1);
                }
                ans.push_back(b[i]);
        }
        else{
            
            ans.push_back(b[i]);
        }
    }
    return ans;
}

int main(){

    int t;
    cin>> t;
    for(int i=0; i<t; i++){

        int n;
        cin>> n;
        vector<int> b(n);
        for(int i=0; i<n; i++){
            
            cin>>b[i];
        }
        vector<int> result = sequence(b, n);
        cout<< result.size() << endl;
        for(int i=0; i<result.size(); i++){
            
            cout<< result[i] << " ";
        }
    }
    return 0;
}