Java 8

` public static int largestRectangle(List h) { int start = 0; int index = 0; int maxArea = 0; Stack stack = new Stack<>();

    for (int i = 0; i < h.size(); i++) {
            int height = h.get(i);
            start = i;
            while (!stack.isEmpty() && stack.peek()[1] > height) {
                    int[] top = stack.pop();
                    index = top[0];
                    int poppedHeight = top[1];
                    maxArea = Math.max(maxArea, poppedHeight * (i - index));
                    start = index;
            }
            stack.push(new int[]{start, height});
    }

    for (int[] pair : stack) {
            int height = pair[1];
            maxArea = Math.max(maxArea, height * (h.size() - pair[0]));
    }

    return maxArea;

} `