1139. Largest 1-Bordered Square

Given a 2D grid of 0s and 1s, return the number of elements in the largest square subgrid that has all 1s on its border, or 0 if such a subgrid doesn't exist in the grid. Example 1: Input: grid = [[1,1,1],[1,0,1],[1,1,1]] Output: 9 Example 2: Input: grid = [[1,1,0,0]] Output: 1 Constraints: - 1 <= grid.length <= 100 - 1 <= grid[0].length <= 100 - grid[i][j] is 0 or 1