42. Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.

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The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image!

Example:

Input: [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6

First

找到最大值，然后进行两次遍历

class Solution(object):
    def trap(self, height):
        """
        :type height: List[int]
        :rtype: int
        """
        if not height: return 0
        ans, tmp = 0, 0

        max_height = (0, height[0])
        for i, v in enumerate(height):
            if v >= max_height[1]:
                max_height = (i, v)
        left = (0, height[0])
        for i, v in enumerate(height[:max_height[0]+1]):
            if v >= left[1]:
                ans += (i-left[0]) * left[1] + tmp
                left = (i, v)
                tmp = 0
            tmp -= v
        tmp, left = 0, (0, height[-1])
        sli = max_height[0] - len(height) - 1
        print sli
        for i, v in enumerate(height[-1:sli:-1]):
            if v >= left[1]:
                ans += (i-left[0]) * left[1] + tmp
                left = (i, v)
                tmp = 0
            tmp -= v
        return ans


s = Solution()
print s.trap([1,0,0,0,2,1,0,4,1,0,3])
print s.trap([4,2,3])