## 题目描述：

LeetCode 533. Lonely Pixel II

Given a picture consisting of black and white pixels, and a positive integer N, find the number of black pixels located at some specific row R and column C that align with all the following rules:

1. Row R and column C both contain exactly N black pixels.
2. For all rows that have a black pixel at column C, they should be exactly the same as row R

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

Example:

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

N = 3
Output: 6
Explanation: All the bold 'B' are the black pixels we need (all 'B's at column 1 and 3).
0    1    2    3    4    5         column index
0    [['W', 'B', 'W', 'B', 'B', 'W'],
1     ['W', 'B', 'W', 'B', 'B', 'W'],
2     ['W', 'B', 'W', 'B', 'B', 'W'],
3     ['W', 'W', 'B', 'W', 'B', 'W']]
row index

Take 'B' at row R = 0 and column C = 1 as an example:
Rule 1, row R = 0 and column C = 1 both have exactly N = 3 black pixels.
Rule 2, the rows have black pixel at column C = 1 are row 0, row 1 and row 2. They are exactly the same as row R = 0.
```

Note:

1. The range of width and height of the input 2D array is [1,200].

## 解题思路：

```利用数组rows，cols分别记录某行、某列'B'像素的个数。

## Python代码：

``````class Solution(object):
def findBlackPixel(self, picture, N):
"""
:type picture: List[List[str]]
:type N: int
:rtype: int
"""
w, h = len(picture), len(picture)
rows, cols =  * w,  * h
for x in range(w):
for y in range(h):
if picture[x][y] == 'B':
rows[x] += 1
cols[y] += 1

sdict = collections.defaultdict(int)
for idx, row in enumerate(picture):
sdict[''.join(row)] += 1

ans = 0
for x in range(w):
row = ''.join(picture[x])
if sdict[row] != N:
continue
for y in range(h):
if picture[x][y] == 'B':
if rows[x] == N:
if cols[y] == N:
ans += 1
return ans
``````

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