Hard · Arrays
Trap rain water
Given an array height of non-negative integers describing an elevation map in which every bar has width 1, return the total units of rain water trapped between the bars after it rains.
Examples
Example 1
[4,2,0,3,2,5]Output: 9 units · O(n)/O(1)
Example 2
[3,0,2,0,4]Output: 7 units · O(n)/O(1)
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