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. Example 1: Input: heights = [2,1,5,6,2,3] Output: 10 Explanation: 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. Example 2: Input: heights = [2,4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104