class Solution {
public:
    typedef pair<int, int> PII;
    int firstCompleteIndex(vector<int>& arr, vector<vector<int>>& mat) {
        int n = mat.size(), m = mat[0].size();
        unordered_map<int, PII> hash;
        for (int i = 0; i < n; i ++ ) 
            for (int j = 0; j < m; j ++ ) 
                hash[mat[i][j]] = {i, j};

        int cnt = arr.size();
        vector<int> c1(cnt, 0), c2(cnt, 0);
        for (int i = 0; i < n * m; i ++ ) {
            auto idx = hash[arr[i]];
            if ( ++ c1[idx.first] == m || ++ c2[idx.second] == n) 
                return i;
        }
        return -1;
  }
};