这个问题好像是2015年百度机试题.

问题描述

给定一个数组a[N],可以画一个柱状图.天上下了一场大雨,这个柱状图里面盛了很多雨水,问盛了多少体积的雨水.要求只扫描一次数组.

样例

1 2 3 输出为0

2 1 4 输出为1

4 1 3 输出为2

思路

类似快速排序,双指针移动

代码

import randomdef another_data():   return [random.randint(0, 10) for i in range(500)]def correct_ans(a):   s = 0   for i in range(len(a)):      left = max(a[0:i]) if i > 0 else 0      right = max(a[i + 1:len(a)]) if i < len(a) - 1 else 0      if min(left, right) < a[i]:         continue      else:         s += min(left, right) - a[i]   return sdef mine(a):   s = 0   ans = 0   left, right = 0, len(a) - 1   while left < right:      # print(a,left,right,ans,s)      if a[left] < a[right]:         i = left         while i < right and a[i] <= a[left]:            s += a[i]            i += 1         ans += (i - left) * min(a[left], a[i]) - s         s = 0         left = i      else:         i = right         while i > left and a[i] <= a[right]:            s += a[i]            i -= 1         ans += (right - i) * min(a[right], a[i]) - s         s = 0         right = i   return ansfor i in range(100):   a = another_data()   assert mine(a) == correct_ans(a)

留个课后思考题,如果是一个二维的数组,求雨水的体积?如果是n维的数组呢?n维数组可以用numpy中的ndarray来表示.