<p>Given an array of integers <code>heights</code> representing the histogram&#39;s bar height where the width of each bar is <code>1</code>, return <em>the area of the largest rectangle in the histogram</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/04/histogram.jpg" style="width: 522px; height: 242px;" />
<pre>
<strong>Input:</strong> heights = [2,1,5,6,2,3]
<strong>Output:</strong> 10
<strong>Explanation:</strong> The above is a histogram where width of each bar is 1.
The largest rectangle is shown in the red area, which has an area = 10 units.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/04/histogram-1.jpg" style="width: 202px; height: 362px;" />
<pre>
<strong>Input:</strong> heights = [2,4]
<strong>Output:</strong> 4
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= heights.length &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= heights[i] &lt;= 10<sup>4</sup></code></li>
</ul>

class Stack{
  private:
    int* data;
    int top;
    int MAXsize;

  public:
    Stack(int size){
      top = -1;
      MAXsize = size;
      data = new int[size];
    };

    bool IsEmpty(){
      return (top == -1);
    };

    int get_top(){
      return data[top];
    };

    bool IsFull(){
      return (top+1 == MAXsize);
    };

    void push(int i){
      if (IsFull()){
        int* new_data = new int[MAXsize * 2];
        for (int j = 0; j <= top; j++){
          new_data[j] = data[j];
        }
        delete[] data;
        data = new_data;
        MAXsize *= 2;
      }
      data[++top] = i;
    };

    int pop(){
      if (IsEmpty()){
        return -1;
      }
      int val = data[top--];
      return val;
    };
};

class Solution {
public:
    int largestRectangleArea(vector<int>& array) {
        int size = array.size();
        Stack* stack = new Stack(size);
        int max_area = 0;

        for (int i = 0; i < size; i++){
            if (stack->IsEmpty() || array[i] > array[stack->get_top()]){
                stack->push(i);
            }
            else if (array[i] <= array[stack->get_top()]){
                while (!(stack->IsEmpty()) && array[i] < array[stack->get_top()]){
                    int position = stack->pop();
                    int height = array[position];
                    int width = (stack->IsEmpty()) ? i : (i - stack->get_top() - 1);

                    int curr_area = height * width;

                    if (curr_area >= max_area){
                        max_area = curr_area;
                    }
                }
                stack->push(i);
            }
        }

        // Cleaning up remaining stack
        while (!(stack->IsEmpty())){
            int position = stack->pop();
            int height = array[position];
            int width = (stack->IsEmpty()) ? size : (size - stack->get_top() - 1);

            int curr_area = height * width;

            if (curr_area >= max_area){
                max_area = curr_area;
            }
        }
        return max_area; // <- This was already correct
    }
};
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