Given an array of integers heights representing the histogram's bar height where the width of each bar is 1 , return the area of the largest rectangle in the histogram .
Examples
Example 1
Input: heights = [2,1,5,6,2,3]
Output: 10
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.
