HDU---1506：Largest Rectangle in a Histogram【单调栈】

Description：

A histogram is a polygon composed of a sequence of rectangles aligned at a common base line. The rectangles have equal widths but may have different heights. For example, the figure on the left shows the histogram that consists of rectangles with the heights 2, 1, 4, 5, 1, 3, 3, measured in units where 1 is the width of the rectangles:

Usually, histograms are used to represent discrete distributions, e.g., the frequencies of characters in texts. Note that the order of the rectangles, i.e., their heights, is important. Calculate the area of the largest rectangle in a histogram that is aligned at the common base line, too. The figure on the right shows the largest aligned rectangle for the depicted histogram.

题解：

枚举每一个单位矩形，那么每一个单位矩形所能构成的最大面积矩形为：从前面第一个比它矮的到它后面第一个比它矮的，单调栈找出两边第一个比它矮的

代码：

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