0084-largest-rectangle-in-histogram.cs

public class Solution {
    public int LargestRectangleArea(int[] heights) {
     int n = heights.Length, max = 0;
        var stack = new Stack<int>();
        for(int i = 0; i <= n; i++)
        {
            var height = i < n ? heights[i] : 0;
            while(stack.Count != 0 && heights[stack.Peek()] > height)
            {
                var currHeight = heights[stack.Pop()];
                var prevIndex = stack.Count == 0 ? -1 : stack.Peek();
                max = Math.Max(max, currHeight * (i - 1 - prevIndex));
            }
            stack.Push(i);
        }
        
        return max;
    }
}