Senior Android Developer

A two-pointer approach can be used for this question. Maintain two indexes. Initialize the first index left as 0 and second index right as n-1, where n is size of the array .
While left < right , do the following : 
a) Keep incrementing index left while arr[left] =0 
b) Keep decrementing index right while arr[right]=1 
c) If left < right then exchange arr[left] and arr[right]

The direct approach to solve this problem is to run two for loops and for every subarray check if it is the maximum sum possible. 
Time complexity: O(N^2), Where N is the size of the array.
Space complexity: O(1)
The efficient approach is to use Kadane's algorithm. It calculates the maximum sum subarray ending at a particular index by using the maximum sum subarray ending at the previous position. 
Steps : 
Declare two variables : currSum which stores maximum sum ending here and maxSum which stores maximum sum so far.
Initialize currSum = 0 and maxSum = INT_MIN.
Now, traverse the array and add the value of the current element to currSum and check : 
1. If currSum > maxSum, update maxSum equals to currSum.
2. If currSum < 0, make currSum equal to zero.
Finally, print the value of maxSum.

The ViewModel class is designed to store and manage UI-related data so that the data survives configuration changes such as screen rotations. — developer.android.com. There are various advantages of using ViewModel class provided by Android framework :
1. Handle configuration changes: ViewModel objects are automatically retained whenever activity is recreated due to configuration changes.
2. Lifecycle Awareness: ViewModel objects are also lifecycle-aware. They are automatically cleared when the Lifecycle they are observing gets permanently destroyed.
3. Data Sharing: Data can be easily shared between fragments in an activity using ViewModels.

RecyclerView is a UI component which allows us to create a scrolling list. It is basically a new ViewGroup used to render any adapter-based view in horizontal/vertical /grid or staggered grid manner using the Viewholder pattern.

Working : So, let’s say when we are scrolling the list which has 50 items in the collection and we show only 5 items at once in the list. Here, item 1 to item 5 is the ones that are visible on the screen. item x is the one that will be loaded next on the screen when we scroll up. All the items here have their own instance of ViewHolder and the ViewHolder here is helpful for caching the specific item’s view. This is how recycling of views happens in recyclerView which is one of the main reasons for the better improvement of recyclerView. In this process, the views of the item are reused to draw new items on the screen.
Similarly, if we have multiple view types, let’s say ViewType1 and ViewType2 then we would have two different collections of scrapped view of type ViewType1 and ViewType2.And while recycling the views, the ViewType1 view will be allocated to only views of ViewType1 and ViewType2 views will be allocated to ViewType2 views.

There are three steps to setting up and using a ViewModel:
1. Separate out your data from your UI controller by creating a class that extends ViewModel
2. Set up communications between your ViewModel and your UI controller
3. Use your ViewModel in your UI controller