Largest Rectangle in Histogram (Variant)

Problem: Given an array of integers representing the heights of bars in a histogram where the width of each bar is 1, find the area of the largest rectangle that can be formed within the histogram.

Constraints: Array length up to 10^5, heights >= 0.

Example: heights = [2,1,5,6,2,3] -> largest rectangle area = 10.

Approach: Use a monotonic increasing stack of indices. For each bar, pop from the stack while the top has a greater height than the current bar, computing the area using the popped height and the width spanned between the new stack top and the current index. O(n) time, O(n) space.