Capture Letter Regions Disconnected from the Board Edge
Company: Amazon
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
Capture every surrounded region of letter `'O'` cells in a rectangular board of `'X'` and `'O'`. Cells connect horizontally or vertically, not diagonally. A region is surrounded exactly when none of its cells touches the board's outer edge. Change all cells in such regions to `'X'`, leaving other cells unchanged.
```cpp
void solve(vector<vector<char>>& board);
```
Mutate the original character matrix; return nothing. Quoted rows below are shorthand for character rows.
### Examples
```text
Input rows: ["XXXXX","XOOXX","XXOXX","OXXOX","XXXXX"]
Rows after call: ["XXXXX","XXXXX","XXXXX","OXXXX","XXXXX"]
```
The left-edge O survives; the other O regions have no edge connection.
```text
Input rows: ["OOO"]
Rows after call: ["OOO"]
```
### Constraints
- Both row and column counts are between 1 and 200.
- Every original cell is `'X'` or `'O'`.
Overview: Capture only O regions disconnected from every border by marking edge-connected cells and mutating the board.
