Maximal Rectangle

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

For example, given the following matrix:

1 0 1 0 01 0 1 1 11 1 1 1 11 0 0 1 0

Return 6.

第一行看作一个直方图，height={1,0,1,0,0}

第二行和第一行看作一个直方图，height={2,0,1,1,1}

第三行和第二行和第一行看作一个直方图，height={3,1,3,2,2}

针对每一个直方图做面积计算，即可