A square grid is symmetric when the value at row r, column c equals the value at row c,
column r for every pair of indices. Given a grid grid, return True if it is square and symmetric,
otherwise False. An empty grid counts as symmetric.
Examples
Input: grid = [[1, 2, 3],
[2, 5, 6],
[3, 6, 9]]
Output: True
Input: grid = [[1, 2],
[3, 1]]
Output: False
Input: grid = [[1, 2, 3]]
Output: False
Explanation: a 1x3 grid is not square.
Constraints
0 <= rows, cols <= 100
Goals
- Compare a cell with its mirror across the main diagonal
- Reject non-square grids before comparing cells