No Member Named Reverse While Using reverse()

Question

    class Solution {
public:
    
    void print (vector<int> array)
    {
        for (int i=0;i<array.size();i++)
        {
            cout<<array[i]<<"  ";
        }
        cout<<endl;
    }
    
    vector<int> nsr(vector<int> heights)
    {
        int n = heights.size();
        vector<int> v(n);
        stack <pair<int,int>> s;  
        
        for (int i=0 ;i<n;i++)
        {
            if (s.size()== 0)
            {
                v.push_back(-1);
            }
            
            else if (s.size()>0 && s.top().first<= heights[i])
            {
                v.push_back (s.top().second);
            }
            
            else if (s.size()>0 && s.top().first >=heights[i])
                
            {
                while (s.size()>0 && s.top().first>= heights[i])
                {
                    s.pop();
                }
                
                if (s.size() == 0)
                    v.push_back(-1);
                else 
                    v.push_back (s.top().second);
            }
                
            s.push({heights[i], i});
        }
     
        return v ;  
    }
    
    vector<int> nsl(vector<int> heights)
    {
 
        int n = heights.size();
        vector<int> v(n);
        print(v);
        stack <pair<int,int>> s;  
        
        for (int i=n-1; i>=0;i--)
        {
            if (s.size()== 0)
            {
                v.push_back(n);
            }
            
            else if (s.size()>0 && s.top().first<= heights[i])
            {  
                v.push_back (s.top().second);
            }
            
            else if (s.size()>0 && s.top().first >=heights[i])
            {
                while (s.size()>0 && s.top().first>= heights[i])
                {
                    s.pop();
                }
                
                if (s.size()== 0)
                    v.push_back(n);
                else 
                    v.push_back (s.top().second);
              
            }
            
            s.push({heights[i], i});
            
        }
       // print (v);
        return v;
  
    }
   
    int largestRectangleArea(vector<int>& heights) {
        
        vector<int> width ;
      
        vector <int> left= nsl(heights);
        left.reverse(left.begin(),left.end());

        vector <int> right = nsr(heights);
        
       // print(left);
       // print(right);
        
        for (int i = 0 ;i< heights.size()-1;i++)
        {
            int element = left[i] - right[i] - 1;
            width.push_back (element);
        }
        
        int area = INT_MIN;
        for (int i =0 ;i<heights.size()-1;i++)
        {
      
            int newarea = heights[i]* width[i];
            area = max(area, newarea);
            //cout<< area <<endl;
            
        }
        
        return area ;
        

        
    }
};

I am using reverse() in vector but it's showing an error. I have tried using header files but the error is same. I had used reverse with vector many times but it never gave an error.

Error :

Line 80: Char 14: error: no member named 'reverse' in 'std::vector<int, std::allocator>' left.reverse(left.begin(),left.end());

Answer 1

There is no member function reverse in the class template std::vector. So this statement

left.reverse(left.begin(),left.end());

is invalid.

You should use the standard algorithm std::reverse declared in the header <algorithm> as for example

reverse(left.begin(),left.end());

There are other problems with your code.

For example in this declaration

vector <int> right = right(heights);

the declared identifier right hides a function right used as an initializer expression. (I suppose that in the right side there is used a call of a function with the name right.) That is in the both sides there is used the vector right. So the declaration does not make a sense.

If you mean the vector right in the both sides then just write

vector<int> right(heights);

Or it is unclear where the name element used in this for loop

for (int i = 0 ;i< heigths.size()-1;i++)
{
    element = left[i] - rigth[i] - 1;
    width.push_back (element);
}

is declared.

Or for example this for loop

for (int i =0 ;i<heights.size()-1;i++)
{
    int area = INT_MIN;
    int newarea = heights[i]* width[i];
    area = max(area, newarea);
    
}

does not find the maximum area.

And moreover outside the loop the name area used in the return statement

return area ;

is undefined.

You need to revise your code entirely from the very beginning.