Measure the Largest All-One Square Area
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
Find the largest square whose cells are all character `'1'` in a rectangular binary matrix, and return its area. Cells containing character `'0'` cannot belong to the square. Return 0 when there is no all-one square.
```cpp
int maximalSquare(vector<vector<char>>& matrix);
```
Quoted rows abbreviate character rows; this is not an integer-cell matrix API.
### Examples
```text
Input rows: ["1110","1110","1111"]
Output: 9
```
```text
Input rows: ["01","10"]
Output: 1
```
### Constraints
- Both dimensions are between 1 and 300.
- Every cell is character `'0'` or `'1'`.
Overview: Compute maximal all-one square area with rolling side-length summaries and correct character-cell semantics.