// Complete the pickingNumbers function below.

int pickingNumbers(vector a) {

int n = a.size();
vector<int> sol(100,0);
//sort(a.begin(), a.end());
for(int i=0; i<n; i++){
    sol[a[i]]++;
}
int pos = max_element(sol.begin(),sol.end()) - sol.begin();
//cout<<sol[pos];
return maxi(sol[pos+1]+sol[pos],sol[pos-1]+sol[pos]);

}

This can be done in linear time.