给定一个仅包含 0 和 1 、大小为 rows x cols 的二维二进制矩阵，找出只包含 1 的最大矩形，并返回其面积。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/maximal-rectangle
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

import java.util.Stack;

class Solution {

    private int solve(int[] height) {
        if (height == null || height.length == 0) {
            return 0;
        }

        int ret = 0;
        Stack<Integer> stack = new Stack<>();
        for (int i = 0; i < height.length; ++i) {
            while (!stack.isEmpty() && height[stack.peek()] >= height[i]) {
                Integer pop = stack.pop();
                ret = Math.max(ret, height[pop] * (i - (stack.isEmpty() ? -1 : stack.peek()) - 1));
            }
            stack.push(i);
        }

        while (!stack.isEmpty()) {
            Integer pop = stack.pop();
            ret = Math.max(ret, height[pop] * (height.length - (stack.isEmpty() ? -1 : stack.peek()) - 1));
        }

        return ret;
    }

    public int maximalRectangle(char[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return 0;
        }

        int ret = 0;
        int[] height = new int[matrix[0].length];
        for (int i = 0; i < matrix.length; ++i) {
            for (int j = 0; j < matrix[0].length; ++j) {
                if (matrix[i][j] == '1') {
                    height[j] += 1;
                } else {
                    height[j] = 0;
                }
            }
            ret = Math.max(ret, solve(height));
        }

        return ret;
    }
}