public static long largestRectangle(List<Integer> h) {
        Stack<Integer> stack = new Stack<>();
        long maxArea = 0;
        int n = h.size();

        for (int i = 0; i < n; i++) {
            while (!stack.isEmpty() && h.get(stack.peek()) >= h.get(i)) {
                int height = h.get(stack.pop());
                int width = stack.isEmpty() ? i : i - stack.peek() - 1;
                maxArea = Math.max(maxArea, (long) height * width);
            }
            stack.push(i);
        }

        while (!stack.isEmpty()) {
            int height = h.get(stack.pop());
            int width = stack.isEmpty() ? n : n - stack.peek() - 1;
            maxArea = Math.max(maxArea, (long) height * width);
        }
        return maxArea;
    }