Swap diagonals

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Time: O(n)

Space: O(1)

Intuition

Swap the two main diagonals of a square matrix.

Algorithm

1For i in 0..n-1: swap mat[i][i] and mat[i][n-1-i].

Common Pitfalls

•Simple O(n) loop swapping primary and secondary diagonal elements.

Swap diagonals.java

Java

// Approach: Swap elements at (i, i) and (i, n-1-i) for each i in [0, n/2) to exchange the two diagonals.
// Time: O(n) Space: O(1)
class Solution {
    public void swapDiagonal(int[][] mat) {
        int n = mat.length - 1;
        for (int i = 0; i <= n; i++) {

            int temp = mat[i][i];
            mat[i][i] = mat[i][n - i];
            mat[i][n - i] = temp;
        }
    }
}

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