POJ http://poj.org/problem?id=2559
LEETCODE https://leetcode-cn.com/problems/largest-rectangle-in-histogram/description/
HDU http://acm.hdu.edu.cn/showproblem.php?pid=1506

LEETCODE https://leetcode-cn.com/problems/largest-rectangle-in-histogram/description/
HDU http://acm.hdu.edu.cn/showproblem.php?pid=1506
