DZY Loves Chessboard · Interview Problem

Codeforces

Easy

Matrices

Strings

DZY Loves Chessboard

Fill the empty cells of a chessboard-like grid so adjacent cells alternate between two characters while preserving the blocked cells.

Acceptance 0%

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Problem Statement

You are given an $n \times m$ board made of characters . and -.

Replace every . with either B or W so that:

no two horizontally or vertically adjacent non-- cells have the same character,
cells marked - must stay unchanged.

The resulting board should form a chessboard-style alternating pattern on all non-blocked cells. Output any valid board.

Input Format

The first line contains two integers $n$ and $m$ .
The next $n$ lines each contain a string of length $m$ describing the board.
Each cell is one of . or -.

Output Format

Print $n$ lines describing a valid board after replacing all . cells with B or W.

Constraints

$1 \le n, m$
The board dimensions are small enough for direct construction.
A valid alternating coloring always exists for the given board.

Examples

Sample cases returned by the problem API.

Example 1

Input

3 4
....
.-..
....

Output

BWBW
W-BW
BWBW

Explanation

Fill each . using a checkerboard coloring. The - cell stays unchanged.

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