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0084.largest-rectangle-in-histogram

题目

Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram.

histogram

Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3].

histogram_area

The largest rectangle is shown in the shaded area, which has area = 10 unit.

For example,
Given heights = [2,1,5,6,2,3],
return 10.

解题思路

这里复制了以下思路:

1、如果已知height数组是升序的,应该怎么做?

比如1,2,5,7,8

那么就是(1*5) vs. (2*4) vs. (5*3) vs. (7*2) vs. (8*1)

也就是max(height[i]*(size-i))

2、使用栈的目的就是构造这样的升序序列,按照以上方法求解。

但是height本身不一定是升序的,应该怎样构建栈?

比如2,1,5,6,2,3

(1)2进栈。s={2}, result = 0

(2)1比2小,不满足升序条件,因此将2弹出,并记录当前结果为2*1=2。

将2替换为1重新进栈。s={1,1}, result = 2

(3)5比1大,满足升序条件,进栈。s={1,1,5},result = 2

(4)6比5大,满足升序条件,进栈。s={1,1,5,6},result = 2

(5)2比6小,不满足升序条件,因此将6弹出,并记录当前结果为6*1=6。s={1,1,5},result = 6

2比5小,不满足升序条件,因此将5弹出,并记录当前结果为5*2=10(因为已经弹出的5,6是升序的)。s={1,1},result = 10

2比1大,将弹出的5,6替换为2重新进栈。s={1,1,2,2,2},result = 10

(6)3比2大,满足升序条件,进栈。s={1,1,2,2,2,3},result = 10

栈构建完成,满足升序条件,因此按照升序处理办法得到上述的max(height[i]*(size-i))=max{3*1, 2*2, 2*3, 2*4, 1*5, 1*6}=8<10

综上所述,result=10

具体的解题过程与上面不同,详见程序注释