Problem A :

1,2,3,4,.......n is an intutive and easy answer.

Difficulty: 5/10 for a A

Problem B

Search the whole matrix a on 2x2 small grids and keep changing the values accordingly till i=0,n-1. j=0,m-1. In the end you will check if the two matrices are now equal or not.

Difficulty: 9/10 for a B

Problem C

There are nine cases totally ABC, ACB, BAC, BCA, CAB, CBA now check for each case seprately and apply binary search to find the lower bound for total_sum/3. Implementation is kinda tough.

Difficulty: 8/10 for a C

Problem D

Just count number of inversions using merge sort/segment tree. If (count1-count2)%2==0 YES else NO. Corner case: check if a & b are a permutation of each other or not.

Difficulty: 5/10 for a D