leetcode 85. Maximal Rectangle

Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing all ones and return its area.

class Solution {
	void get_bigger(vector<vector<char>>& matrix, int leftupX, int leftupY, int&maxsquare)
	{
		int kxmin = -1; bool xup(true), yup(true);
		for (int ky = 0; ky + leftupY < matrix.size(); ky++)
		{
			if (matrix[ky + leftupY][leftupX] == '0')
				break;
			int kx = 0;
			while (leftupX + kx<matrix[0].size()&&matrix[ky + leftupY][leftupX + kx]=='1')
				kx++;
			kx--;
			if (kxmin == -1)
				kxmin = kx;
			if (kx < kxmin)
				kxmin = kx;
			if ((1 + kxmin)*(1 + ky)>maxsquare)
				maxsquare = (1 + kxmin)*(1 + ky);
		}
	}
public:
	int maximalRectangle(vector<vector<char>>& matrix) {
		if (matrix.empty())
			return 0;
		if (matrix[0].empty())
			return 0;
		int maxarea = 0;
		for (int i = 0; i < matrix.size(); i++)
			for (int j = 0; j < matrix[0].size(); j++)
			{
				if (matrix[i][j] == '1')
				{
					get_bigger(matrix, j, i, maxarea);
				}
			}
		return maxarea;
	}
};

accepted