1139. Largest 1-Bordered Square

https://leetcode.com/problems/largest-1-bordered-square

Description

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

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