How to print array elements above and below minor dioganal? - c++

Question

I need your help. In C++ there is a two dimensional array. How to print array elements above and below minor dioganal?
I need to print array elements above minor diognal with minor dioganal elements
elements above minor dioganal:
For example :
1 2 3
4 5 6
7 8 9
The output should be:
1 2 3
4 5
7
1 2 3 4 5 7 in any order.
elements below minor dioganal:
Output should be:
3
5 6
7 8 9
3 5 6 7 8 9 in any order.

Answer 1

This should be rather simple.
For above minor diagonal, we need to print in the first row all values, then one less, then one less and so on.
For below minor diagonal, we need to print in the first row starting with column offset 3, then one less, then one less and so on.
For printing, we will use stateful lambdas.
Including the generation of some test data and some debug output the programm will be very small.
Please see:
#include <iostream>
#include <string>
#include <iterator>
#include <vector>
#include <algorithm>
#include <numeric>
constexpr size_t Dimension = 3U;
int main() {
// Define 2D vector of requested size
std::vector<std::vector<int>> array(Dimension, std::vector<int>(Dimension));
// Fill with some consecutive test values
std::for_each(array.begin(), array.end(), [i = 1](std::vector<int>& v) mutable {
std::iota(v.begin(), v.end(), i); i += Dimension; });
// Show result for above minor diagonal
std::cout << "\n\nAbove minor:\n\n";
std::for_each(array.begin(), array.end(), [o = Dimension](std::vector<int>& v) mutable {
std::copy_n(v.begin() , o, std::ostream_iterator<int>(std::cout, " ")); --o;});
// Show result for below minor diagonal
std::cout << "\n\nBelow minor:\n\n";
std::for_each(array.begin(), array.end(), [o = (Dimension-1)](std::vector<int> & v) mutable {
std::copy(v.begin()+o, v.end(), std::ostream_iterator<int>(std::cout, " ")); --o;});
return 0;
}