Lonely Pixel I

Given a picture consisting of black and white pixels, find the number of black lonely pixels.

The picture is represented by a 2D char array consisting of 'B' and 'W', which means black and white pixels respectively.

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

Example:

Input: 
[['W', 'W', 'B'],
 ['W', 'B', 'W'],
 ['B', 'W', 'W']]

Output: 3
Explanation: All the three 'B's are black lonely pixels.

Note:

1. The range of width and height of the input 2D array is [1,500].

public class Solution {
    public int findLonelyPixel(char[][] picture) {
        if (picture == null || picture[0] == null) return 0;
        
        int m = picture.length, n = picture[0].length;
        boolean[] rows = new boolean[m];
        Arrays.fill(rows, true);
        boolean[] cols = new boolean[n];
        Arrays.fill(cols, true);
        
        for (int i = 0; i < m; i++) {
            int rowCount = 0;
            for (int j = 0; j < n; j++) {
                if (picture[i][j] == 'B')
                    rowCount++;
            }
            if (rowCount > 1) rows[i] = false;
        }
        
        for (int j = 0; j < n; j++) {
            int colCount = 0;
            for (int i = 0; i < m; i++) {
                if (picture[i][j] == 'B')
                    colCount++;
            }
            if (colCount > 1) cols[j] = false;
        }
        
        int result = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (picture[i][j] == 'B' && rows[i] && cols[j])
                    result++;
            }
        }
        return result;
    }
}