% default stuff
clear; clc; clf;

% this is the original height of 3*5 land
land = [1 2 3 4 5;
        2 3 4 5 6;
        7 7 7 7 7];
% visualize the original landscape first =)
surf(land) % or you can use 'mesh'

% this is the desired height of that 3*5 land
desired_height = input('What is your desired flat land height (in m): ');
desired = repmat(desired_height,3,5);

% show the desired flat landscape!
hold on % do google search/browse Matlab help to understand what is this
surf(desired) % aha, you see overlapping figures now
hold off

% now the computation part, in step by step fashion
% we want to know the height difference in each square meter!
%
% since the required solution is the 'minimum' amount of soil to be
% added or removed, then we must use soil from a square that is
% 'higher' from the desired height and dump it into square that is
% 'lower'  than the desired height.
difference = desired - land; 
columnSum = sum(difference); % we sum column by column
% this is the amount of soil to be added (if positive)
% or removed (if it is negative)
finalAnswer = sum(columnSum);
% you can also write all in one line, like this:
% finalAnswer = sum(sum(desired-land));

% to make the output a little bit nicer, use 'if', 'disp', and 'sprintf'
if finalAnswer > 0 % positive, means add
  disp(sprintf('We need to add %d m^3 soil', finalAnswer));
else % negative, means remove, make the answer positive!
  disp(sprintf('We need to remove %d m^3 soil', -finalAnswer));
end

% challenge:
%   play around with mesh/surf function, it is a powerful
%   visualization tool!