in two traversal-
  
vector<int> getSecondOrderElements(int n, vector<int> a)
{
    int mini=INT_MAX;
    int maxi=INT_MIN;
    for(int i=0  ; i<n ; i++)
    {
        if(a[i]>maxi)
        {
            maxi=a[i];
        }
        if(a[i]<mini)
        {
            mini=a[i];
        }
    }
    vector<int>ans;
    int mi=INT_MAX;
    int ma=INT_MIN;
    for(int i=0 ; i<n ; i++)
    {
        if(a[i]>ma and a[i]!=maxi)
        {
              ma=a[i];
            
        }
        if(a[i]<mi and a[i]!=mini)
        {
            mi=a[i];
        }
    }
    ans.push_back(ma);
    ans.push_back(mi);
    return ans;
}

in single traversal-
  
int findSecondLargest(int n, vector<int> &arr)
{
    int largest=INT_MIN;
    int secondlargest=INT_MIN;
    for(int i=0 ; i<n ; i++)
    {
        if(arr[i]>largest)
        {
            secondlargest=largest;
            largest=arr[i];
        }
        if(arr[i]<largest and arr[i]>secondlargest)
        {
            secondlargest=arr[i];
        }
    }
    if(secondlargest==INT_MIN)
    {
        return -1;
    }
    return secondlargest;
}