• Time:O(mn)
• Space:O(mn)

## C++

``````class Solution {
public:
int findBlackPixel(vector<vector<char>>& picture, int target) {
const int m = picture.size();
const int n = picture[0].size();
int ans = 0;
vector<int> rows(m);
vector<int> cols(n);
vector<string> rowStrings(m);
unordered_map<string, int> countRowStrings;

for (int i = 0; i < m; ++i) {
string s;
for (int j = 0; j < n; ++j) {
if (picture[i][j] == 'B') {
++rows[i];
++cols[j];
}
s += picture[i][j];
}
rowStrings[i] = s;
++countRowStrings[s];
}

for (int i = 0; i < m; ++i)
if (rows[i] == target && countRowStrings[rowStrings[i]] == target)
for (int j = 0; j < n; ++j)
if (picture[i][j] == 'B' && cols[j] == target)
++ans;

return ans;
}
};
``````

## JAVA

``````class Solution {
public int findBlackPixel(char[][] picture, int target) {
final int m = picture.length;
final int n = picture[0].length;
int ans = 0;
int[] rows = new int[m];
int[] cols = new int[n];
String[] rowStrings = new String[m];
Map<String, Integer> countRowStrings = new HashMap<>();

for (int i = 0; i < m; ++i) {
StringBuilder sb = new StringBuilder();
for (int j = 0; j < n; ++j) {
if (picture[i][j] == 'B') {
++rows[i];
++cols[j];
}
sb.append(picture[i][j]);
}
rowStrings[i] = sb.toString();
countRowStrings.merge(rowStrings[i], 1, Integer::sum);
}

for (int i = 0; i < m; ++i)
if (rows[i] == target && countRowStrings.get(rowStrings[i]) == target)
for (int j = 0; j < n; ++j)
if (picture[i][j] == 'B' && cols[j] == target)
++ans;

return ans;
}
}
``````

## Python

``````class Solution:
def findBlackPixel(self, picture: List[List[str]], target: int) -> int:
m = len(picture)
n = len(picture[0])
ans = 0
rows = [row.count('B') for row in picture]
cols = [col.count('B') for col in zip(*picture)]
rowStrings = [''.join(row) for row in picture]
countRowStrings = Counter(rowStrings)

for i, (row, stringRow) in enumerate(zip(rows, rowStrings)):
if row == target and countRowStrings[stringRow] == target:
for j, col in enumerate(cols):
if picture[i][j] == 'B' and col == target:
ans += 1

return ans
``````