0531. Lonely Pixel I

https://leetcode.com/problems/lonely-pixel-i

Description

Given an m x n picture consisting of black 'B' and white 'W' pixels, return the number of black lonely pixels.

A black lonely pixel is a character 'B' that located at a specific position where the same row and same column don't have any other black pixels.

Example 1:

**Input:** picture = [["W","W","B"],["W","B","W"],["B","W","W"]]
**Output:** 3
**Explanation:** All the three 'B's are black lonely pixels.

Example 2:

**Input:** picture = [["B","B","B"],["B","B","W"],["B","B","B"]]
**Output:** 0

Constraints:

• m == picture.length

• n == picture[i].length

• 1 <= m, n <= 500

• picture[i][j] is 'W' or 'B'.

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