Solution.java

class Solution {
    public int findBlackPixel(char[][] picture, int target) {
        int m = picture.length, n = picture[0].length;
        int[] rows = new int[m];
        Map<Integer, List<Integer>> cols = new HashMap<>();
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (picture[i][j] == 'B') {
                    ++rows[i];
                    cols.computeIfAbsent(j, k -> new ArrayList<>()).add(i);
                }
            }
        }
        boolean[][] t = new boolean[m][m];
        for (int i = 0; i < m; ++i) {
            for (int k = i; k < m; ++k) {
                t[i][k] = i == k || all(picture[i], picture[k]);
                t[k][i] = t[i][k];
            }
        }
        int res = 0;
        for (int i = 0; i < m; ++i) {
            if (rows[i] == target) {
                for (int j = 0; j < n; ++j) {
                    List<Integer> col = cols.get(j);
                    if (col != null && col.size() == target) {
                        boolean check = true;
                        for (int k : col) {
                            check = check && t[i][k];
                        }
                        if (check) {
                            ++res;
                        }
                    }
                }
            }
        }
        return res;
    }

    private boolean all(char[] row1, char[] row2) {
        int n = row1.length;
        for (int j = 0; j < n; ++j) {
            if (row1[j] != row2[j]) {
                return false;
            }
        }
        return true;
    }
}