|
| 1 | +""" |
| 2 | +Problem Link: https://leetcode.com/problems/trapping-rain-water/ |
| 3 | + |
| 4 | +Given n non-negative integers representing an elevation map where the width of each bar is 1, |
| 5 | +compute how much water it can trap after raining. |
| 6 | + |
| 7 | +Example 1: |
| 8 | +Input: height = [0,1,0,2,1,0,1,3,2,1,2,1] |
| 9 | +Output: 6 |
| 10 | +Explanation: The above elevation map (black section) is represented by array |
| 11 | +[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. |
| 12 | + |
| 13 | +Example 2: |
| 14 | +Input: height = [4,2,0,3,2,5] |
| 15 | +Output: 9 |
| 16 | + |
| 17 | +Constraints: |
| 18 | +n == height.length |
| 19 | +1 <= n <= 2 * 104 |
| 20 | +0 <= height[i] <= 105 |
| 21 | +""" |
| 22 | +class Solution: |
| 23 | + def trap(self, height: List[int]) -> int: |
| 24 | + max_left = [height[0]] |
| 25 | + |
| 26 | + for index in range(1, len(height)): |
| 27 | + max_left.append(max(max_left[-1], height[index])) |
| 28 | + |
| 29 | + max_right = [0] * len(height) |
| 30 | + max_right[-1] = height[-1] |
| 31 | + |
| 32 | + for index in range(len(height) - 2, -1, -1): |
| 33 | + max_right[index] = max(max_right[index+1], height[index]) |
| 34 | + |
| 35 | + total_water = 0 |
| 36 | + for index in range(len(height)): |
| 37 | + total_water += min(max_left[index], max_right[index]) - height[index] |
| 38 | + |
| 39 | + return total_water |
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