Practice Surrounded Regions

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Medium#130

LeetCode Problem

Surrounded Regions

Array Depth-First Search Breadth-First Search Union Find Matrix

Problem Statement

In the board of X and O cells, connect O cells using horizontal or vertical neighbors only. A connected group is surrounded when none of its cells touches the outer border. Change all O cells in such groups to X in the original board. Leave border-connected O groups unchanged. The operation is in place and does not require a return value.

Source: Surrounded Regions on LeetCode. Use the original task for its coding environment and submissions.

Examples

# Example 1

Input

board = [["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]]

Output

[["X","X","X","X"],["X","X","X","X"],["X","X","X","X"],["X","O","X","X"]]

# Example 2

Input

board = [["X"]]

Output

[["X"]]

Constraints

m == board.length

n == board[i].length

1 <= m, n <= 200

board[i][j] is 'X' or 'O'.

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