Given a boolean 2D array, where each row is sorted. Find the row with the maximum number of 1s.

Example 1:

Input:
N = 3, M = 4
Mat[] = {{0 1 1 1},
         {0 0 1 1},
         {0 0 1 1}}
Output: 0
Explanation: Row 0 has 3 ones whereas
rows 1 and 2 have just 2 ones.

​Example 2:

Input: 
N = 2, M = 2
Mat[] = {{0 1},
         {1 1}}
Output: 1
Explanation: Row 1 has 2 ones whereas
row 0 has just a single one. 

Your Task:
You don't need to read input or print anything. Your task is to complete the function maxOnes () which takes a 2D array Mat[][] and its dimensions N and M as inputs and returns the row index with the maximum number of 1s (0-based index). If there are multiple rows with the maximum number of ones, then return the row with the smaller index.

Expected Time Complexity: O(NLogM).
Expected Auxiliary Space: O(1).

Constraints:
1 <= N, M <= 40
0 <= M[ ][ ] <= 1