# 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
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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++

 `// C++ program to replace the value of the middle element  ` `// of the matrix with the sum of surrounding elements ` ` `  `#include ` `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; ` `} `

## Java

 `// 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 ` `} `

## Python3

 `# 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 `

## C#

 `// 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); ` `    ``} ` `    `  `} `

## PHP

 ` `

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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