public static long largestRectangle(List<int> h) => 
        GetMaxArea(h, 0, h.Count()-1);
    
    private static long GetMaxArea(List<int> h, int l, int r) {
        if (l > r) return 0;
        if (l == r) return h[l];
        int min = int.MaxValue;
        int minIndex = -1;
        for (int i = l; i <= r; i++) {
            if (h[i] < min) {
                min = h[i];
                minIndex = i;
            }
        }
        long area = (r - l + 1) * min;
        long leftArea = GetMaxArea(h, l, minIndex-1);
        long rightArea = GetMaxArea(h, minIndex+1, r);
        return Math.Max(area, Math.Max(leftArea, rightArea));
    }