Sort a matrix by the sum of the rows - c++

Question

I have to sort the matrix by the sum of the rows, the smallets sum has to be first and the the bigger and at the end has to be the biggest sum.
I have done this but I can't finish it:
#include <iostream>
using namespace std;
int main ()
{
int **matrix;
int i, j, count, row, col, sum, temp;
cout << "\n Enter the number of rows and columns";
cin >> row >> col;
matrix = new int *[row];
for (count = 0; count < row; count++)
matrix[count] = new int[col];
cout << "\nNow enter the element for the matrix.";
for (i = 0; i < row; i++)
{
for (j = 0; j < col; j++)
{
cout << "\nRow " << (i + 1) << " Col " << (j + 1) << " :";
cin >> *(*(matrix + i) + j);
}
}
for (i = 0; i < row; i++)
{
sum = 0;
for (j = 0; j < col; j++)
sum = sum + matrix[i][j];
cout << sum << endl;
}
for (int count = 0; count < row; count++)
delete[]matrix[count];
delete[]matrix;
matrix = 0;
return 0;
}

Answer 1

You can use standard algorithms std::sort and std::accumulate. Below there is a demonstrative program that shows how these algorithms can be used together.
#include <iostream>
#include <algorithm>
#include <numeric>
#include <cstdlib>
#include <ctime>
int main()
{
const size_t M = 3, N = 5;
std::srand( ( unsigned int )std::time( nullptr ) );
int **matrix = new int *[M];
for ( size_t i = 0; i < M; i++ ) matrix[i] = new int[N];
for ( size_t i = 0; i < M; i++ )
{
for ( size_t j = 0; j < N; j++ ) matrix[i][j] = std::rand() % ( M * N );
}
for ( size_t i = 0; i < M; i++ )
{
for ( size_t j = 0; j < N; j++ ) std::cout << matrix[i][j] << ' ';
std::cout << '\n';
}
std::cout << '\n';
auto sort_by_sum = [N]( const auto &left, const auto &right )
{
return std::accumulate( left, left + N, 0ll ) <
std::accumulate( right, right + N, 0ll );
};
std::sort( matrix, matrix + M, sort_by_sum );
for ( size_t i = 0; i < M; i++ )
{
for ( size_t j = 0; j < N; j++ ) std::cout << matrix[i][j] << ' ';
std::cout << '\n';
}
std::cout << '\n';
return 0;
}
The program output might look like
11 2 4 14 0
9 7 9 4 14
10 7 5 0 7
10 7 5 0 7
11 2 4 14 0
9 7 9 4 14