Sorting 2D Array C++

Question

Is it possible to sort a 2D Array using qsort or std::sort in C++ such that the elements are in increasing order when read from left to right in each row or from top to bottom in each column?

For example,

13, 14, 15, 16
1, 4, 3, 2
7, 5, 7, 6
9, 10, 11, 12

Becomes:

{ 1, 2, 3, 4 }
{ 5, 6, 7, 8 }
{ 9, 10, 11, 12 }
{ 13, 14, 15, 16 } 

I know you can do it by creating two comparison functions and then first sorting each row then comparing the first elements of each row to establish the columns, but is there a way to do it in one function itself?

Answer 1

Yes. C++ STL library is built with separation of algorithms and containers. What links them together is iterators. Raw pointer is iterator, therefore it is possible to initialize vector with raw pointers and then sort that vector as usual.

std::vector<int> v(arr2d, arr2d + N); // create a vector based on pointers
                                      // This assumes array is contiguous range 
                                      // in memory, N=number of elemnts in arr2d
// using default comparison (operator <):
std::sort (v.begin(), v.end());

// cout by 4 elements in a row

Answer 2

First Make a 2D vector .

Sort each vector in this 2D vector

Sort the whole vector

Code :

#include <iostream>
#include <vector>
#include <algorithm>

template <class T>
void Sort2dArray(std::vector<std::vector<T>> & numbers)
{

    for(auto & i : numbers){//sort each vector<T> in numbers
        std::sort(i.begin(),i.end());
    }
    std::sort(numbers.begin(),numbers.end(),[](//sort numbers by defining custom compare 
              const std::vector<T>& a,const std::vector<T>&b){
        for(int i=0;i<a.size()&&i<b.size();i++)
        {
            if(a[i]>b[i])
                return false;
            else if(a[i]<b[i])
                return true;
        }
        return a.size()<b.size() ? true : false;
    });
}

int main()
{
    std::vector<std::vector<int>> numbers={ {13, 14, 15, 16},
                                            {1, 4, 3, 2},
                                            {8, 5, 7, 6},
                                            {9, 10, 12,11}};
    Sort2dArray(numbers);//sort array

    //write sorted array
    for(auto i:numbers)
    {
        for(auto j:i)
            std::cout<<j<<" ";
        std::cout<<"\n";
    }
}

Answer 3

# include <iostream>
using namespace std ;


void swap (int &x , int &y)
{
    int temp = x ;
    x = y ;
    y = temp ;
}

void main ()
{
    int arr [3][3] = {{90,80,70},{60,50,40},{30,100,10}} ;
    int x ;

    for (int k = 0; k < 3; k++)
    {
        for (int m = 0; m < 3; m++)
        {
            x = m+1;
            for (int i = k; i < 3 ; i++)
            {
                for (int j = x; j < 3; j++)
                {
                    if (arr [k][m] > arr [i][j])
                        swap(arr [k][m] ,arr [i][j]);
                }
                x=0;
            } 
        }
    }

    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            cout << arr [i][j] << " ";
        }
    }


    system("pause");
}

C++ Sorting 2-D array ascendingly

Answer 4

**Sorting 2D array in c++**

#include <iostream>

using namespace std;

int main()
{
    int i,j,k,m,temp,n,limit;
    int** p;


    cout<<"Enter the limit:";
    cin>>limit;

    p=new int*[limit];

//inputing
    for(i=0;i<limit;i++)
    {
        p[i] = new int[limit];

        for(j=0;j<limit;j++)
        {
          cin>>p[i][j];
        }

    }

//sorting
    for(i=0;i<limit;i++)
    {
        for(j=0;j<limit;j++)
        {
            if (j==limit-1 && i<limit-1)
            {
                n =-1;
                m=i+1;
            }
            else
            {
                m=i;
                n=j;
            }

            for(k=n+1;k<limit;k++)
            {
                if(p[i][j] > p[m][k] )
                {
                    temp = p[i][j];
                    p[i][j] = p[m][k];
                    p[m][k] = temp;
                }

                if(k==limit-1 && m<limit-1) { m++;  k=-1;  }

            }
        }
    }

    //displaying
    for(i=0;i<limit;i++)
    {
        for(j=0;j<limit;j++)
        {
            cout<<p[i][j]<<endl;
        }

    }

    return 0;
}

Answer 5

In theory you should be able to input the 16 numbers into an array. Use a for loop, maybe even a nested one, to sort the numbers. Then as for output you want the ascending numbers in four groups of four?

cout<<Vector[0]<<Vector[1]<<Vector[2]<<Vector[3]<<endl;
cout<<Vector[4]<<Vector[5]<<Vector[6]<<Vector[7]<<endl;
cout<<Vector[8]<<Vector[9]<<Vector[10]<<Vector[11]<<endl;
cout<<Vector[12]<<Vector[13]<<Vector[14]<<Vector[15]<<endl;

very arbitrary but I'm not quite sure of the question.