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Trap Rain Water

Solution Approach
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HardarrayExpected: O(n) time, O(1) space
two-pointersstack

Problem

Given n non-negative integers representing an elevation map, compute how much water it can trap after raining.

Example 1:

Input: height = [0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]
Output: 6
Explanation: 6 units of water are trapped between the bars.

Example 2:

Input: height = [4, 2, 0, 3, 2, 5]
Output: 9
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