Maximal Rectangle

Given a `rows x cols` binary matrix filled with `'0'`s and `'1'`s, find the largest rectangle containing only `'1'`s and return its area. **Example 1:** ``` Input: matrix = [ ["1","0","1","0","0"], ["1","0","1","1","1"], ["1","1","1","1","1"], ["1","0","0","1","0"] ] Output: 6 ``` **Example 2:** ``` Input: matrix = [["0"]] Output: 0 ``` **Example 3:** ``` Input: matrix = [["1"]] Output: 1 ```