HardArrays
Trapping Rain Water
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Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
Examples
Example 1
Input
height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output
6
Water fills the valleys between bars. The total trapped water is 6 units.
Example 2
Input
height = [4,2,0,3,2,5]
Output
9
Water fills the gaps between the tall bars on each side, trapping 9 units total.
Example 3
Input
height = [1,0,1]
Output
1
One unit of water is trapped between the two bars of height 1.
Constraints
- n == height.length
- 1 <= n <= 2 * 104
- 0 <= height[i] <= 105
Optimal complexity
Time
O(n)
Space
O(1)
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