221\. Maximal Square

Medium

Given an `m x n` binary `matrix` filled with `0`'s and `1`'s, _find the largest square containing only_ `1`'s _and return its area_.

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/11/26/max1grid.jpg)

**Input:** matrix = [["1","0","1","0","0"],["1","0","1","1","1"],["1","1","1","1","1"],["1","0","0","1","0"]]

**Output:** 4 

**Example 2:**

![](https://assets.leetcode.com/uploads/2020/11/26/max2grid.jpg)

**Input:** matrix = [["0","1"],["1","0"]]

**Output:** 1 

**Example 3:**

**Input:** matrix = [["0"]]

**Output:** 0 

**Constraints:**

*   `m == matrix.length`
*   `n == matrix[i].length`
*   `1 <= m, n <= 300`
*   `matrix[i][j]` is `'0'` or `'1'`.