Maximal Rectangle

class Solution {
public:
    int maximalRectangle( vector<vector<char>> &matrix ) {
        if( matrix.empty() ) { return 0; }
        int n = matrix[0].size();
        vector<int> H( n, 0 );
        vector<int> L( n, 0 );
        vector<int> R( n, n );
        int ret = 0;
        for( int i = 0; i < matrix.size(); ++i ) {
            int left = 0, right = n;
            for( int j = 0; j < n; ++j ) {
                if( matrix[i][j] == ‘0‘ ) {
                    H[j] = 0; L[j] = 0; R[j] = n;
                    left = j+1;
                } else {
                    ++H[j];
                    L[j] = max( L[j], left );
                }
            }
            for( int j = n-1; j >= 0; --j ) {
                if( matrix[i][j] == ‘0‘ ) {
                    right = j;
                } else {
                    R[j] = min( R[j], right );
                    ret = max( ret, (R[j]-L[j])*H[j] );
                }
            }
        }
        return ret;
    }
};