```
class Solution {
public:
int findLonelyPixel(vector<vector<char>>& picture) {
int res = 0;
int m = picture.size();
if (m == 0) return res;
int n = picture[0].size();
vector<int> row(m, 0), col(n, 0);
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (picture[i][j] == 'B') {
row[i]++;
col[j]++;
}
}
}
for (int i = 0; i < m; i++) {
if (row[i] != 1) continue; // early termination to save time
for (int j = 0; j < n; j++) {
if (picture[i][j] == 'B' && col[j] == 1) res++;
}
}
return res;
}
};
```