Grokking Data Structures & Algorithms for Coding Interviews
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Problem 2: Matrix Diagonal Sum (easy)
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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

  1. Example 1:
    • Input: 
      [[1,2,3],
 [4,5,6],
 [7,8,9]]
    • Expected Output: 25
    • Justification: Summing up the two diagonals (1+5+9+3+7), we get 25. Please note that the element at [1][1] = 5 is counted only once.
  2. Example 2:
    • Input: 
      [[1,0],
 [0,1]]
    • Expected Output: 2
    • Justification: The sum of the two diagonals is 1+1 = 2.
  3. Example 3:
    • Input: 
      [[5]]
    • Expected Output: 5
    • Justification: Since there's only one element, it is the sum itself.

Constraints:

  • n == mat.length == mat[i].length
  • 1 <= n <= 100
  • 1 <= mat[i][j] <= 100

Try it yourself

Try solving this question here:

Python3
Python3
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