链接
给定一个由 0 和 1 组成的矩阵 matrix ，找出只包含 1 的最大矩形，并返回其面积。

注意：此题 matrix 输入格式为一维 01 字符串数组。

import java.util.Stack;

class Solution {

    private static int getMax(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();
                int left = stack.isEmpty() ? -1 : stack.peek();
                ret = Math.max(ret, (i - left - 1) * height[pop]);
            }
            stack.push(i);
        }

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

        return ret;
    }

    public static int maximalRectangle(String[] matrix) {
        if (matrix == null || matrix.length == 0) {
            return 0;
        }
        int n = matrix.length;
        int m = matrix[0].length();
        int[] height = new int[m];
        int ret = 0;
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < m; ++j) {
                height[j] = matrix[i].charAt(j) == '1' ? 1 + height[j] : 0;
            }
            ret = Math.max(ret, getMax(height));
        }
        return ret;
    }

    public static void main(String[] args) {
        String[] matrix = {"10100", "10111", "11111", "10010"};
        System.out.println(maximalRectangle(matrix));

    }
}