# Fill missing entries of a magic square

• Difficulty Level : Medium
• Last Updated : 09 Sep, 2022

Given a 3X3 matrix mat with it’s left diagonal elements missing (set to 0), considering the sum of every row, column and diagonal of the original matrix was equal, the task is to find the missing diagonal elements and print the original matrix.

Examples:

Input: mat[][] = {{0, 7, 6}, {9, 0, 1}, {4, 3, 0}}
Output:
2 7 6
9 5 1
4 3 8
Row sum = Column sum = Diagonal sum = 15

Input: mat[][] = {{0, 1, 1}, {1, 0, 1}, {1, 1, 0}}
Output:
1 1 1
1 1 1
1 1 1

Approach: Let Sum denote the total sum excluding the diagonal elements,

Sum = total sum of the given matrix – diagonalSum
Sum = (3 * rowSum) – diagonalSum
Sum = (2 * rowSum) [Since, columnSum = rowSum = diagonalSum]
rowSum = Sum / 2

Hence, we can insert an element in every row such that the sum of the row is rowSum

Below is the implementation of the above approach:

## C++

 `// C++ program to fill blanks with numbers``#include ``using` `namespace` `std;` `// Function to print the original matrix``int` `printFilledDiagonal(``int` `sq[][3])``{``    ``// Calculate the sum of all the elements``    ``// of the matrix``    ``int` `sum = 0;``    ``for` `(``int` `i = 0; i < 3; i++)``        ``for` `(``int` `j = 0; j < 3; j++)``            ``sum += sq[i][j];` `    ``// Required sum of each row (from the approach)``    ``sum /= 2;` `    ``for` `(``int` `i = 0; i < 3; i++) {` `        ``// Row sum excluding the diagonal element``        ``int` `rowSum = 0;``        ``for` `(``int` `j = 0; j < 3; j++)``            ``rowSum += sq[i][j];` `        ``// Element that must be inserted at``        ``// diagonal element of the current row``        ``sq[i][i] = sum - rowSum;``    ``}` `    ``// Print the updated matrix``    ``for` `(``int` `i = 0; i < 3; i++) {``        ``for` `(``int` `j = 0; j < 3; j++)``            ``cout << sq[i][j] << ``" "``;``        ``cout << endl;``    ``}``}` `// Driver Program to test above function``int` `main()``{``    ``int` `sq[3][3] = {``        ``{ 0, 7, 6 },``        ``{ 9, 0, 1 },``        ``{ 4, 3, 0 }``    ``};` `    ``printFilledDiagonal(sq);``    ``return` `0;``}`

## Java

 `// Java program to fill blanks with numbers` `import` `java.io.*;` `class` `GFG {``   `   `// Function to print the original matrix``static` `int` `printFilledDiagonal(``int` `sq[][])``{``    ``// Calculate the sum of all the elements``    ``// of the matrix``    ``int` `sum = ``0``;``    ``for` `(``int` `i = ``0``; i < ``3``; i++)``        ``for` `(``int` `j = ``0``; j < ``3``; j++)``            ``sum += sq[i][j];` `    ``// Required sum of each row (from the approach)``    ``sum /= ``2``;` `    ``for` `(``int` `i = ``0``; i < ``3``; i++) {` `        ``// Row sum excluding the diagonal element``        ``int` `rowSum = ``0``;``        ``for` `(``int` `j = ``0``; j < ``3``; j++)``            ``rowSum += sq[i][j];` `        ``// Element that must be inserted at``        ``// diagonal element of the current row``        ``sq[i][i] = sum - rowSum;``    ``}` `    ``// Print the updated matrix``    ``for` `(``int` `i = ``0``; i < ``3``; i++) {``        ``for` `(``int` `j = ``0``; j < ``3``; j++)``            ``System.out.print( sq[i][j] + ``" "``);``        ``System.out.println();``    ``}``    ``return` `0``;``}` `// Driver Program to test above function` `    ``public` `static` `void` `main (String[] args) {``        ``int` `sq[][] = {``        ``{ ``0``, ``7``, ``6` `},``        ``{ ``9``, ``0``, ``1` `},``        ``{ ``4``, ``3``, ``0` `}``    ``};` `    ``printFilledDiagonal(sq);``    ``}``    ` `}``// This code is contributed by anuj_67..`

## Python3

 `# Python3 program to fill blanks``# with numbers` `# Function to print the original matrix``def` `printFilledDiagonal(sq):` `    ``# Calculate the sum of all the``    ``# elements of the matrix``    ``Sum` `=` `0``    ``for` `i ``in` `range``(``0``, ``3``):``        ``for` `j ``in` `range``(``0``, ``3``):``            ``Sum` `+``=` `sq[i][j]` `    ``# Required sum of each``    ``# row (from the approach)``    ``Sum` `=` `Sum``/``/``2` `    ``for` `i ``in` `range``(``0``, ``3``):` `        ``# Row sum excluding the``        ``# diagonal element``        ``rowSum ``=` `0``        ``for` `j ``in` `range``(``0``, ``3``):``            ``rowSum ``+``=` `sq[i][j]` `        ``# Element that must be inserted``        ``# at diagonal element of the``        ``# current row``        ``sq[i][i] ``=` `Sum` `-` `rowSum``    ` `    ``# Print the updated matrix``    ``for` `i ``in` `range``(``0``, ``3``):``        ``for` `j ``in` `range``(``0``, ``3``):``            ``print``(sq[i][j], end ``=` `" "``)``        ``print``()` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:` `    ``sq ``=` `[[``0``, ``7``, ``6``],``          ``[``9``, ``0``, ``1``],``          ``[``4``, ``3``, ``0``]]` `    ``printFilledDiagonal(sq)``    ` `# This code is contributed``# by Rituraj Jain`

## C#

 `// C# program to fill blanks with numbers` `using` `System;` `class` `GFG {``    `   `// Function to print the original matrix``static` `int` `printFilledDiagonal(``int` `[,]sq)``{``    ``// Calculate the sum of all the elements``    ``// of the matrix``    ``int` `sum = 0;``    ``for` `(``int` `i = 0; i < 3; i++)``        ``for` `(``int` `j = 0; j < 3; j++)``            ``sum += sq[i,j];` `    ``// Required sum of each row (from the approach)``    ``sum /= 2;` `    ``for` `(``int` `i = 0; i < 3; i++) {` `        ``// Row sum excluding the diagonal element``        ``int` `rowSum = 0;``        ``for` `(``int` `j = 0; j < 3; j++)``            ``rowSum += sq[i,j];` `        ``// Element that must be inserted at``        ``// diagonal element of the current row``        ``sq[i,i] = sum - rowSum;``    ``}` `    ``// Print the updated matrix``    ``for` `(``int` `i = 0; i < 3; i++) {``        ``for` `(``int` `j = 0; j < 3; j++)``            ``Console.Write( sq[i,j] + ``" "``);``            ``Console.WriteLine();``    ``}``    ``return` `0;``}` `// Driver Program to test above function` `    ``public` `static` `void` `Main () {``        ``int` `[,]sq = {``        ``{ 0, 7, 6 },``        ``{ 9, 0, 1 },``        ``{ 4, 3, 0 }``    ``};` `    ``printFilledDiagonal(sq);``    ``}``    ` `}``// This code is contributed by inder_verma`

## PHP

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## Javascript

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Output

```2 7 6
9 5 1
4 3 8
```

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