# Php Program to Find difference between sums of two diagonals

• Last Updated : 06 Jan, 2022

Given a matrix of n X n. The task is to calculate the absolute difference between the sums of its diagonal.
Examples:

```Input : mat[][] = 11 2 4
4 5 6
10 8 -12
Output : 15
Sum of primary diagonal = 11 + 5 + (-12) = 4.
Sum of primary diagonal = 4 + 5 + 10 = 19.
Difference = |19 - 4| = 15.

Input : mat[][] = 10 2
4 5
Output : 7```

Calculate the sums across the two diagonals of a square matrix. Along the first diagonal of the matrix, row index = column index i.e mat[i][j] lies on the first diagonal if i = j. Along the other diagonal, row index = n – 1 – column index i.e mat[i][j] lies on the second diagonal if i = n-1-j. By using two loops we traverse the entire matrix and calculate the sum across the diagonals of the matrix.
Below is the implementation of this approach:

## PHP

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Output:

`15`

Time complexity : O(n*n)
We can optimize above solution to work in O(n) using the patterns present in indexes of cells.

## PHP

 ``

Output:

`15`

Time complexity : O(n)
Please refer complete article on Find difference between sums of two diagonals for more details!

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