Lonely Pixel I

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原文链接：http://www.cnblogs.com/amazingzoe/p/6661168.html

本文介绍了一种算法，用于在一个由黑白像素组成的二维数组中找到所有‘孤独’的黑色像素。孤独像素是指那些在同一行和同一列中没有其他黑色像素的黑色像素。

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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:

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

 1 public class Solution {
 2     public int findLonelyPixel(char[][] picture) {
 3         if (picture == null || picture[0] == null) return 0;
 4         
 5         int m = picture.length, n = picture[0].length;
 6         boolean[] rows = new boolean[m];
 7         Arrays.fill(rows, true);
 8         boolean[] cols = new boolean[n];
 9         Arrays.fill(cols, true);
10         
11         for (int i = 0; i < m; i++) {
12             int rowCount = 0;
13             for (int j = 0; j < n; j++) {
14                 if (picture[i][j] == 'B')
15                     rowCount++;
16             }
17             if (rowCount > 1) rows[i] = false;
18         }
19         
20         for (int j = 0; j < n; j++) {
21             int colCount = 0;
22             for (int i = 0; i < m; i++) {
23                 if (picture[i][j] == 'B')
24                     colCount++;
25             }
26             if (colCount > 1) cols[j] = false;
27         }
28         
29         int result = 0;
30         for (int i = 0; i < m; i++) {
31             for (int j = 0; j < n; j++) {
32                 if (picture[i][j] == 'B' && rows[i] && cols[j])
33                     result++;
34             }
35         }
36         return result;
37     }
38 }