Max sum submatrix in row and column wise

#1

approach for max sum submatrix in row and column wise sorted matrix is not clear.
how he is creating suffix sum matrix and generating the answer ??

#2

in the sum submatrix array
(i,j)th cell contains the sum of submatrix from (i,j) to (n-1,m-1)

which thing is not clear
approach is discussed in video
plz watch the video again if didn’t understand

#3

why prefix matrix is not used?

#4

to optimised the solution

if we use loop based approach then time complexity will be O(n^4)
but if we use prefix sum array then time complexity will be O(n^2)