LeetCode 1572: Matrix Diagonal Sum Solution

Master LeetCode problem 1572 (Matrix Diagonal Sum), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1572. Matrix Diagonal Sum

Easy

Array Matrix

Problem Explanation

Explanation

To solve this problem, we need to iterate through the elements of the given square matrix and calculate the sum of the primary diagonal and the secondary diagonal excluding the overlapping element. We can achieve this by maintaining two pointers for the primary diagonal and the secondary diagonal. We iterate through the matrix and update the sum based on the current element's position.

For the primary diagonal, the indices of the elements are when i == j.
For the secondary diagonal, the indices of the elements are when i + j == n - 1, where n is the size of the matrix.

After calculating the sum of both diagonals, we return the total sum as the result.

Time Complexity: O(n), where n is the size of the matrix. Space Complexity: O(1)

Solution Code

class Solution {
    public int diagonalSum(int[][] mat) {
        int n = mat.length;
        int sum = 0;
        for (int i = 0; i < n; i++) {
            sum += mat[i][i]; // primary diagonal
            sum += mat[i][n - 1 - i]; // secondary diagonal
        }
        if (n % 2 == 1) {
            sum -= mat[n/2][n/2]; // Exclude the middle element if the matrix has an odd size
        }
        return sum;
    }
}

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