Solution.java

class Solution {
    public int findBlackPixel(char[][] picture, int target) {
        int m = picture.length;
        int n = picture[0].length;
        List<Integer>[] g = new List[n];
        Arrays.setAll(g, k -> new ArrayList<>());
        int[] rows = new int[m];
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (picture[i][j] == 'B') {
                    ++rows[i];
                    g[j].add(i);
                }
            }
        }
        int ans = 0;
        for (int j = 0; j < n; ++j) {
            if (g[j].isEmpty() || (rows[g[j].get(0)] != target)) {
                continue;
            }
            int i1 = g[j].get(0);
            int ok = 0;
            if (g[j].size() == rows[i1]) {
                ok = target;
                for (int i2 : g[j]) {
                    if (!Arrays.equals(picture[i1], picture[i2])) {
                        ok = 0;
                        break;
                    }
                }
            }
            ans += ok;
        }
        return ans;
    }
}