```
int findLonelyPixel(vector<vector<char>>& picture) {
int m = picture.size(), n = m? picture[0].size() : 0, cnt = 0;
if(!m || !n) return cnt;
vector<int> cols(n,0); vector<int> rows(m,0);
for(int i = 0; i < m; ++i)
for(int j = 0; j < n; ++j)
if(picture[i][j] == 'B'){
cols[j]++;
rows[i]++;
}
for(int i = 0; i < m; ++i){
if(rows[i] != 1) continue;
for(int j = 0; j < n; ++j){
if(cols[j] != 1) continue;
if(picture[i][j] == 'B') cnt++;
}
}
return cnt;
}
```