# Sum of matrix in which each element is absolute difference of its row and column numbers

Given a positive integer **n**. Consider a matrix of **n** rows and **n** columns, in which each element contain absolute difference of its row number and numbers. The task is to calculate sum of each element of the matrix.**Examples :**

Input : n = 2 Output : 2 Matrix formed with n = 2 with given constraint: 0 1 1 0 Sum of matrix = 2. Input : n = 3 Output : 8 Matrix formed with n = 3 with given constraint: 0 1 2 1 0 1 2 1 0 Sum of matrix = 8.

**Method 1 (Brute Force):**

Simply construct a matrix of n rows and n columns and initialize each cell with absolute difference of its corresponding row number and column number. Now, find the sum of each cell.

Below is the implementation of above idea :

## C++

`// C++ program to find sum of matrix in which each` `// element is absolute difference of its corresponding` `// row and column number row.` `#include<bits/stdc++.h>` `using` `namespace` `std;` `// Return the sum of matrix in which each element` `// is absolute difference of its corresponding row` `// and column number row` `int` `findSum(` `int` `n)` `{` ` ` `// Generate matrix` ` ` `int` `arr[n][n];` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `for` `(` `int` `j = 0; j < n; j++)` ` ` `arr[i][j] = ` `abs` `(i - j);` ` ` `// Compute sum` ` ` `int` `sum = 0;` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `for` `(` `int` `j = 0; j < n; j++)` ` ` `sum += arr[i][j];` ` ` `return` `sum;` `}` `// Driven Program` `int` `main()` `{` ` ` `int` `n = 3;` ` ` `cout << findSum(n) << endl;` ` ` `return` `0;` `}` |

## Java

`// Java program to find sum of matrix` `// in which each element is absolute` `// difference of its corresponding` `// row and column number row.` `import` `java.io.*;` `public` `class` `GFG {` `// Return the sum of matrix in which` `// each element is absolute difference` `// of its corresponding row and column` `// number row` `static` `int` `findSum(` `int` `n)` `{` ` ` ` ` `// Generate matrix` ` ` `int` `[][]arr = ` `new` `int` `[n][n];` ` ` `for` `(` `int` `i = ` `0` `; i < n; i++)` ` ` `for` `(` `int` `j = ` `0` `; j < n; j++)` ` ` `arr[i][j] = Math.abs(i - j);` ` ` `// Compute sum` ` ` `int` `sum = ` `0` `;` ` ` `for` `(` `int` `i = ` `0` `; i < n; i++)` ` ` `for` `(` `int` `j = ` `0` `; j < n; j++)` ` ` `sum += arr[i][j];` ` ` `return` `sum;` `}` ` ` `// Driver Code` ` ` `static` `public` `void` `main (String[] args)` ` ` `{` ` ` `int` `n = ` `3` `;` ` ` `System.out.println(findSum(n));` ` ` `}` `}` `// This code is contributed by vt_m.` |

## Python3

`# Python3 program to find sum of matrix` `# in which each element is absolute` `# difference of its corresponding` `# row and column number row.` `# Return the sum of matrix in which each` `# element is absolute difference of its` `# corresponding row and column number row` `def` `findSum(n):` ` ` `# Generate matrix` ` ` `arr ` `=` `[[` `0` `for` `x ` `in` `range` `(n)]` ` ` `for` `y ` `in` `range` `(n)]` ` ` `for` `i ` `in` `range` `(n):` ` ` `for` `j ` `in` `range` `(n):` ` ` `arr[i][j] ` `=` `abs` `(i ` `-` `j)` ` ` `# Compute sum` ` ` `sum` `=` `0` ` ` `for` `i ` `in` `range` `(n):` ` ` `for` `j ` `in` `range` `(n):` ` ` `sum` `+` `=` `arr[i][j]` ` ` `return` `sum` `# Driver Code` `if` `__name__ ` `=` `=` `"__main__"` `:` ` ` `n ` `=` `3` ` ` `print` `(findSum(n))` ` ` `# This code is contributed by ita_c` |

## C#

`// C# program to find sum of matrix` `// in which each element is absolute` `// difference of its corresponding` `// row and column number row.` `using` `System;` `public` `class` `GFG {` `// Return the sum of matrix in which` `// each element is absolute difference` `// of its corresponding row and column` `// number row` `static` `int` `findSum(` `int` `n)` `{` ` ` `// Generate matrix` ` ` `int` `[,]arr = ` `new` `int` `[n, n];` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `for` `(` `int` `j = 0; j < n; j++)` ` ` `arr[i,j ] = Math.Abs(i - j);` ` ` ` ` `// Compute sum` ` ` `int` `sum = 0;` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `for` `(` `int` `j = 0; j < n; j++)` ` ` `sum += arr[i, j];` ` ` ` ` `return` `sum;` `}` ` ` `// Driver Code` ` ` `static` `public` `void` `Main(String[] args)` ` ` `{` ` ` `int` `n = 3;` ` ` `Console.WriteLine(findSum(n));` ` ` `}` `}` `// This code is contributed by vt_m.` |

## PHP

`<?php` `// PHP program to find sum of` `// matrix in which each element` `// is absolute difference of` `// its corresponding row and` `// column number row.` `// Return the sum of matrix` `// in which each element` `// is absolute difference` `// of its corresponding row` `// and column number row` `function` `findSum( ` `$n` `)` `{` ` ` ` ` `// Generate matrix` ` ` `$arr` `=` `array` `(` `array` `());` ` ` `for` `(` `$i` `= 0; ` `$i` `< ` `$n` `; ` `$i` `++)` ` ` `for` `(` `$j` `= 0; ` `$j` `< ` `$n` `; ` `$j` `++)` ` ` `$arr` `[` `$i` `][` `$j` `] = ` `abs` `(` `$i` `- ` `$j` `);` ` ` `// Compute sum` ` ` `$sum` `= 0;` ` ` `for` `(` `$i` `= 0; ` `$i` `< ` `$n` `; ` `$i` `++)` ` ` `for` `(` `$j` `= 0; ` `$j` `< ` `$n` `; ` `$j` `++)` ` ` `$sum` `+= ` `$arr` `[` `$i` `][` `$j` `];` ` ` `return` `$sum` `;` `}` ` ` `// Driver Code` ` ` `$n` `= 3;` ` ` `echo` `findSum(` `$n` `);` `// This code is contributed by anuj_67.` `?>` |

## Javascript

`<script>` `// Javascript program to find sum of matrix` `// in which each element is absolute` `// difference of its corresponding` `// row and column number row.` ` ` ` ` `// Return the sum of matrix in which` ` ` `// each element is absolute difference` ` ` `// of its corresponding row and column` ` ` `// number row` ` ` `function` `findSum(n)` ` ` `{` ` ` ` ` `// Generate matrix` ` ` `let arr=` `new` `Array(n);` ` ` `for` `(let i = 0; i < n; i++)` ` ` `{` ` ` `arr[i] = ` `new` `Array(n);` ` ` `for` `(let j = 0; j < n; j++)` ` ` `{` ` ` `arr[i][j] = 0;` ` ` `}` ` ` `}` ` ` ` ` `for` `(let i = 0; i < n; i++)` ` ` `for` `(let j = 0; j < n; j++)` ` ` `arr[i][j] = Math.abs(i - j);` ` ` ` ` `// Compute sum` ` ` `let sum = 0;` ` ` `for` `(let i = 0; i < n; i++)` ` ` `for` `(let j = 0; j < n; j++)` ` ` `sum += arr[i][j];` ` ` ` ` `return` `sum;` ` ` `}` ` ` ` ` `// Driver Code` ` ` `let n = 3;` ` ` `document.write(findSum(n));` ` ` ` ` `// This code is contributed by avanitrachhadiya2155` ` ` `</script>` |

**Output: **

8

**Method 2 (O(n)):**

Consider n = 3, matrix formed will be:

0 1 2

1 0 1

2 1 0

Observe, the main diagonal is always 0 since all i are equal to j. The diagonal just above and just below will always be 1 because at each cell either i is 1 greater than j or j is 1 greater than i and so on.

Following the pattern we can see that the total sum of all the elements in the matrix will be, for each i from 0 to n, add i*(n-i)*2.

Below is the implementation of above idea :

## C++

`// C++ program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `#include<bits/stdc++.h>` `using` `namespace` `std;` `// Return the sum of matrix in which each` `// element is absolute difference of its` `// corresponding row and column number row` `int` `findSum(` `int` `n)` `{` ` ` `int` `sum = 0;` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `sum += i*(n-i);` ` ` `return` `2*sum;` `}` `// Driven Program` `int` `main()` `{` ` ` `int` `n = 3;` ` ` `cout << findSum(n) << endl;` ` ` `return` `0;` `}` |

## Java

`// Java program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `import` `java.io.*;` `class` `GFG {` `// Return the sum of matrix in which each` `// element is absolute difference of its` `// corresponding row and column number row` `static` `int` `findSum(` `int` `n)` `{` ` ` `int` `sum = ` `0` `;` ` ` `for` `(` `int` `i = ` `0` `; i < n; i++)` ` ` `sum += i * (n - i);` ` ` `return` `2` `* sum;` `}` ` ` `// Driver Code` ` ` `static` `public` `void` `main(String[] args)` ` ` `{` ` ` `int` `n = ` `3` `;` ` ` `System.out.println(findSum(n));` ` ` `}` `}` `// This code is contributed by vt_m.` |

## C#

`// C# program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `using` `System;` `class` `GFG {` `// Return the sum of matrix in which each` `// element is absolute difference of its` `// corresponding row and column number row` `static` `int` `findSum(` `int` `n)` `{` ` ` `int` `sum = 0;` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `sum += i * (n - i);` ` ` `return` `2 * sum;` `}` ` ` `// Driver Code` ` ` `static` `public` `void` `Main(String[] args)` ` ` `{` ` ` `int` `n = 3;` ` ` `Console.WriteLine(findSum(n));` ` ` `}` `}` `// This code is contributed by vt_m.` |

## Python3

`# Python 3 program to find sum` `# of matrix in which each element` `# is absolute difference of its` `# corresponding row and column` `# number row.` `# Return the sum of matrix in` `# which each element is absolute` `# difference of its corresponding` `# row and column number row` `def` `findSum(n):` ` ` `sum` `=` `0` ` ` `for` `i ` `in` `range` `(n):` ` ` `sum` `+` `=` `i ` `*` `(n ` `-` `i)` ` ` `return` `2` `*` `sum` `# Driver code` `n ` `=` `3` `print` `(findSum(n))` `# This code is contributed by Shrikant13` |

## PHP

`<?php` `// PHP program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `// Return the sum of matrix in which each` `// element is absolute difference of its` `// corresponding row and column number row` `function` `findSum(` `$n` `)` `{` ` ` `$sum` `= 0;` ` ` `for` `( ` `$i` `= 0; ` `$i` `< ` `$n` `; ` `$i` `++)` ` ` `$sum` `+= ` `$i` `* (` `$n` `- ` `$i` `);` ` ` `return` `2 * ` `$sum` `;` `}` ` ` `// Driver Code` ` ` `$n` `= 3;` ` ` `echo` `findSum(` `$n` `);` `// This code is contributed by anuj_67.` `?>` |

## Javascript

`<script>` `// Java script program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `// Return the sum of matrix in which each` `// element is absolute difference of its` `// corresponding row and column number row` `function` `findSum( n)` `{` ` ` `let sum = 0;` ` ` `for` `(let i = 0; i < n; i++)` ` ` `sum += i * (n - i);` ` ` `return` `2 * sum;` `}` ` ` `// Driver Code ` ` ` `let n = 3;` ` ` `document.write(findSum(n));` `// This code is contributed by mohan pavan` `</script>` |

Output:

8

**Method 3 (Trick):**

Consider n = 3, matrix formed will be:

0 1 2

1 0 1

2 1 0

So, sum = 1 + 1 + 1 + 1 + 2 + 2.

On Rearranging, 1 + 2 + 1 + 2 + 2 = 1 + 2 + 1 + 2^{2}.

So, in every case we can rearrange the sum of matrix so that the answer always will be sum of first n – 1 natural number and sum of square of first n – 1 natural number.

Sum of first n natural number = ((n)*(n + 1))/2. Sum of first n natural number = ((n)*(n + 1)*(2*n + 1)/6.

Below is the implementation of above idea :

## C++

`// C++ program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `#include<bits/stdc++.h>` `using` `namespace` `std;` `// Return the sum of matrix in which each element` `// is absolute difference of its corresponding` `// row and column number row` `int` `findSum(` `int` `n)` `{` ` ` `n--;` ` ` `int` `sum = 0;` ` ` `sum += (n*(n+1))/2;` ` ` `sum += (n*(n+1)*(2*n + 1))/6;` ` ` `return` `sum;` `}` `// Driven Program` `int` `main()` `{` ` ` `int` `n = 3;` ` ` `cout << findSum(n) << endl;` ` ` `return` `0;` `}` |

## Java

`// Java program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `import` `java.io.*;` `public` `class` `GFG {` ` ` `// Return the sum of matrix in which each element` `// is absolute difference of its corresponding` `// row and column number row` `static` `int` `findSum(` `int` `n)` `{` ` ` `n--;` ` ` `int` `sum = ` `0` `;` ` ` `sum += (n * (n + ` `1` `)) / ` `2` `;` ` ` `sum += (n * (n + ` `1` `) * (` `2` `* n + ` `1` `)) / ` `6` `;` ` ` `return` `sum;` `}` ` ` `// Driver Code` ` ` `static` `public` `void` `main (String[] args)` ` ` `{` ` ` `int` `n = ` `3` `;` ` ` `System.out.println(findSum(n));` ` ` `}` `}` `// This code is contributed by vt_m.` |

## Python3

`# Python 3 program to find sum of matrix` `# in which each element is absolute` `# difference of its corresponding row` `# and column number row.` `# Return the sum of matrix in which` `# each element is absolute difference` `# of its corresponding row and column` `# number row` `def` `findSum(n):` ` ` `n ` `-` `=` `1` ` ` `sum` `=` `0` ` ` `sum` `+` `=` `(n ` `*` `(n ` `+` `1` `)) ` `/` `2` ` ` `sum` `+` `=` `(n ` `*` `(n ` `+` `1` `) ` `*` `(` `2` `*` `n ` `+` `1` `)) ` `/` `6` ` ` `return` `int` `(` `sum` `)` `# Driver Code` `n ` `=` `3` `print` `(findSum(n))` `# This code contributed by Rajput-Ji` |

## C#

`// C# program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` `using` `System;` `public` `class` `GFG {` ` ` `// Return the sum of matrix in which each element` `// is absolute difference of its corresponding` `// row and column number row` `static` `int` `findSum(` `int` `n)` `{` ` ` `n--;` ` ` `int` `sum = 0;` ` ` `sum += (n * (n + 1)) / 2;` ` ` `sum += (n * (n + 1) * (2 * n + 1)) / 6;` ` ` `return` `sum;` `}` ` ` `// Driver Code` ` ` `static` `public` `void` `Main(String[] args)` ` ` `{` ` ` `int` `n = 3;` ` ` `Console.WriteLine(findSum(n));` ` ` `}` `}` `// This code is contributed by vt_m.` |

## PHP

`<?php` `// PHP program to find sum of` `// matrix in which each element` `// is absolute difference of its` `// corresponding row and column` `// number row.` `// Return the sum of matrix in` `// which each element is absolute` `// difference of its corresponding` `// row and column number row` `function` `findSum(` `$n` `)` `{` ` ` `$n` `--;` ` ` `$sum` `= 0;` ` ` `$sum` `+= (` `$n` `* (` `$n` `+ 1)) / 2;` ` ` `$sum` `+= (` `$n` `* (` `$n` `+ 1) *` ` ` `(2 * ` `$n` `+ 1)) / 6;` ` ` `return` `$sum` `;` `}` `// Driver Code` `$n` `= 3;` `echo` `findSum(` `$n` `) ;` `// This code is contributed` `// by nitin mittal.` `?>` |

## Javascript

`<script>` `// Java script program to find sum of matrix in which` `// each element is absolute difference of its` `// corresponding row and column number row.` ` ` `// Return the sum of matrix in which each element` `// is absolute difference of its corresponding` `// row and column number row` `function` `findSum( n)` `{` ` ` `n--;` ` ` `let sum = 0;` ` ` `sum += (n * (n + 1)) / 2;` ` ` `sum += (n * (n + 1) * (2 * n + 1)) / 6;` ` ` `return` `sum;` `}` ` ` `// Driver Code` ` ` `let n = 3;` ` ` `document.write(findSum(n));` ` ` `// This code is contributed by mohan pavan` `</script>` |

**Output :**

8

**Source:**

https://stackoverflow.com/questions/42043708/sum-of-matrix-in-which-each-element-is-absolute-difference-of-row-and-column

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