Replace the middle element of matrix with sum of surrounding elements

Given a square matrix mat[][] of odd dimensions, the task is to change the value of the middle most element of the matrix to the sum of the elements surrounding it.

Examples:

Input: 
mat[][] = { {2, 1, 7}, 
            {3, 7, 2}, 
            {5, 4, 9} }
Output:
2 1 7
3 10 2
5 4 9

Input: 
mat[][] = {{1, 3, 5, 6, 7},
           {3, 5, 3, 2, 1},
           {1, 2, 3, 4, 5},
           {7, 9, 2, 1, 6},
           {9, 1, 5, 3, 2} }
Output: 
1 3 5 6 7
3 5 3 2 1
1 2 11 4 5
7 9 2 1 6
9 1 5 3 2

Approach: The middle element of the matrix of odd order will be located at the position mat[n / 2][n / 2].



Therefore directly update the element as:

mat[n / 2][n / 2] = mat[n / 2 - 1][n / 2]
                  + mat[n / 2][n / 2 - 1]
                  + mat[n / 2 + 1][n / 2]
                  + mat[n / 2][n / 2 + 1]

Below is the implementation of the above approach:

C++

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// C++ program to replace the value of the middle element 
// of the matrix with the sum of surrounding elements
  
#include <iostream>
using namespace std;
const int MAX = 100;
  
// Function to print the matrix
void print(int mat[][MAX], int n)
{
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cout << mat[i][j] << " ";
        }
        cout << endl;
    }
}
  
// Function to change the value of the middle element 
// of the matrix to the sum of surrounding elements
void changemiddle(int mat[][MAX], int n)
{
    // Change the middle element
    mat[n / 2][n / 2]
        = mat[n / 2 - 1][n / 2]
          + mat[n / 2][n / 2 - 1]
          + mat[n / 2 + 1][n / 2]
          + mat[n / 2][n / 2 + 1];
  
    // Function call to print the matrix
    print(mat, n);
}
  
// Driver code
int main()
{
    int mat[][MAX] = { { 2, 1, 7 },
                       { 3, 7, 2 },
                       { 5, 4, 9 } };
  
    changemiddle(mat, 3);
  
    return 0;
}

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Java

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// Java program to replace the value of the middle element 
// of the matrix with the sum of surrounding elements\
  
public class GFG{
      
    // Function to print the matrix
    static void print(int mat[][], int n)
    {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                System.out.print(mat[i][j] + " ");
            }
             System.out.println();
        }
    }
      
    // Function to change the value of the middle element 
    // of the matrix to the sum of surrounding elements
    static void changemiddle(int mat[][], int n)
    {
        // Change the middle element
        mat[n / 2][n / 2]
            = mat[n / 2 - 1][n / 2]
              + mat[n / 2][n / 2 - 1]
              + mat[n / 2 + 1][n / 2]
              + mat[n / 2][n / 2 + 1];
      
        // Function call to print the matrix
        print(mat, n);
    }
      
    // Driver code
    public static void main(String []args)
    {
        int mat[][] = { { 2, 1, 7 },
                           { 3, 7, 2 },
                           { 5, 4, 9 } };
      
        changemiddle(mat, 3);
    }
    // This code is contributed by Ryuga
}

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Python3

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# Python3 program to replace the value
# of the middle element of the matrix 
# with the sum of surrounding elements 
  
MAX = 100
  
# Function to print the matrix 
def printMatrix(mat, n): 
  
    for i in range(n): 
        for j in range(n): 
            print(mat[i][j], end = " "
          
        print()
  
# Function to change the value of 
# the middle element of the matrix
# to the sum of surrounding elements 
def changemiddle(mat, n):
  
    # Change the middle element 
    mat[n // 2][n // 2] = (mat[n // 2 - 1][n // 2] + 
                           mat[n // 2][n // 2 - 1] + 
                           mat[n // 2 + 1][n // 2] + 
                           mat[n // 2][n // 2 + 1])
  
    # Function call to print the matrix 
    printMatrix(mat, n) 
  
# Driver Code
if __name__ == "__main__"
  
    mat = [ [ 2, 1, 7 ], 
            [ 3, 7, 2 ], 
            [ 5, 4, 9 ]] 
  
    changemiddle(mat, 3)
  
# This code is contributed 
# by rituraj_jain

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C#

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// C# program to replace the value of the middle element 
// of the matrix with the sum of surrounding elements\
   
using System;
public class GFG{
       
    // Function to print the matrix
    static void print(int[,] mat, int n)
    {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                Console.Write(mat[i,j] + " ");
            }
             Console.Write("\n");
        }
    }
       
    // Function to change the value of the middle element 
    // of the matrix to the sum of surrounding elements
    static void changemiddle(int[,] mat, int n)
    {
        // Change the middle element
        mat[n / 2,n / 2]
            = mat[n / 2 - 1,n / 2]
              + mat[n / 2,n / 2 - 1]
              + mat[n / 2 + 1,n / 2]
              + mat[n / 2,n / 2 + 1];
       
        // Function call to print the matrix
        print(mat, n);
    }
       
    // Driver code
    public static void Main()
    {
        int[,] mat = { { 2, 1, 7 },
                           { 3, 7, 2 },
                           { 5, 4, 9 } };
       
        changemiddle(mat, 3);
    }
     
}

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PHP

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<?php
// PHP program to replace the value of 
// the middle element of the matrix 
// with the sum of surrounding elements
  
// Function to print the matrix
function printmat(&$mat, $n)
{
    for ($i = 0; $i < $n; $i++)
    {
        for ($j = 0; $j < $n; $j++) 
        {
            echo ($mat[$i][$j]);
            echo (" ");
        }
        echo ("\n");
    }
}
  
// Function to change the value of the
// middle element of the matrix to the
// sum of surrounding elements
function changemiddle(&$mat, $n)
{
    // Change the middle element
    $mat[$n / 2][$n / 2] = $mat[$n / 2 - 1][$n / 2] + 
                           $mat[$n / 2][$n / 2 - 1] + 
                           $mat[$n / 2 + 1][$n / 2] + 
                           $mat[$n / 2][$n / 2 + 1];
  
    // Function call to print the matrix
    printmat($mat, $n);
}
  
// Driver code
$mat = array(array(2, 1, 7),
             array(3, 7, 2),
             array(5, 4, 9));
  
changemiddle($mat, 3);
  
// This code is contributed 
// by Shivi_Aggarwal 
?>

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Output:

2 1 7 
3 10 2 
5 4 9

Time Complexity : O(n * m), Here n is No. of Rows and m is No. of Colum.



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