Lintcode 363. Trapping Rain Water (Medium) (Python)

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解决如何计算降雨后地面上能收集多少雨水的问题。通过双指针法，分别从左右两端开始扫描，记录最大高度并计算可收集的水量。

Trapping Rain Water

Description:

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.

Trapping Rain Water

Example
Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.

Challenge
O(n) time and O(1) memory

O(n) time and O(n) memory is also acceptable.

Code:

class Solution:
    """
    @param heights: a list of integers
    @return: a integer
    """
    def trapRainWater(self, heights):
        # write your code here
        highLeft,  highRight, res = 0, 0, 0
        lh = len(heights)
        print("mark0")
        high = [[0, 0] for i in range (lh)]
        print("mark")
        for i in range(lh):
            highLeft = max(highLeft, heights[i])
            high[i][0] = highLeft
        for i in range(lh):
            highRight = max(highRight, heights[lh-1-i])
            high[lh-1-i][1] = highRight
        for i in range(len(high)):
            res += min(high[i])-heights[i]
        return res