42. Trapping Rain Water LeetCode

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.

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])