Problem 2: Matrix Diagonal Sum (easy)

Problem Statement

Given a square matrix (2D array), calculate the sum of its two diagonals.

The two diagonals in consideration are the primary diagonal that spans from the top-left to the bottom-right and the secondary diagonal that spans from top-right to bottom-left. If a number is part of both diagonals (which occurs only for odd-sized matrices), it should be counted only once in the sum.

Examples

Example 1:
- Input:
```
[[1,2,3],
 [4,5,6],
 [7,8,9]]
```
- Expected Output: 25

.....

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Fabrice L

· 2 years ago

You don't need to iterate over the entire array, you can just get half of it and retrieve values from the 4 "corners", and then add the middle point in case of a odd number of rows.

class Solution {
    diagonalSum(mat) {
        let totalSum = 0;  // Initialize the total sum
        const len = mat.length;
        for (let i = 0; i < Math.floor(len / 2); i += 1) {
            totalSum += ( mat[i][i] + 
							            mat[i][len - 1 - i] + 
							            mat[len - 1 - i][i] + 
							            mat[len - 1 - i][len - 1 - i]
						            );
        }
        if (len % 2 === 1) {
            // add center
            let pt = Math.floor(len / 2);
            totalSum += mat[pt][pt];
        }
        return totalSum;  // Return the calculated total sum
    }
}

Naman Jindal

· 2 years ago

 diagonalSum(mat) {
        let totalSum = 0;  // Initialize the total sum
        let n = mat.length;
        // ToDo: Write Your Code Here.//[[5]]
        for(let i = 0; i < n ; i++){
            if(i !== n-i-1){
                totalSum+=(mat[i][i] + mat[i][n-1-i])
            }else{
                totalSum+=mat[i][i]
            }
        }
        return totalSum;  // Return the calculated total sum
    }

Andrew Sologor

· a year ago

func diagonalSum(mat [][]int) int {
  totalSum := 0
  
  i := 0
  j := len(mat) - 1

  for j >= 0 {
    totalSum += mat[i][i]
    
    if i != j {
      totalSum += mat[i][j]
    }

    i++
    j--
  }

  return totalSum
}

luke.rickard

· 3 years ago

anyone else getting this error when trying to run this ?

Unknown Error - Check your Input

kimsuyon2013

· 3 years ago

Leopoldo Hernandez

· 2 years ago

"""
My solution:
Time Complexity:
The time complexity is O(n),
where n is the number of elements in a row.
The function iterates through each row and performs constant-time
operations for each element.
Space Complexity:
The space complexity is O(1).
The function uses a constant amount of space regardless
of the input size.
There are only a few variables (total_sum, diagonal_top_to_bottom_sum, diagonal_bottom_to_top_sum, matrix_length) used.
"""
class Solution:
    def diagonalSum(self, mat):
        total_sum = 0  # Initialize the total sum
        diagonal_top_to_bottom_sum = 0
        diagonal_bottom_to_top_sum = 0
        matrix_length = len(mat[0])  # provide length of elements in row
        print(f"matrix_length: {matrix_length}")
        for row_idx, row in enumerate(mat):