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.
Example 1:
Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6
Explanation: The elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1].
In this case, 6 units of rain water are being trapped.
Example 2:
Input: height = [4,2,0,3,2,5]
Output: 9
Explanation: 9 units of rain water are trapped between the bars.
Examples
Example 1
Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6
Explanation: 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
Explanation: Water fills the gaps between the tall bars on each side, trapping 9 units total.
Example 3
Input: height = [1,0,1]
Output: 1
Explanation: One unit of water is trapped between the two bars of height 1.
Constraints
- -n == height.length
- -1 <= n <= 2 * 10^4
- -0 <= height[i] <= 10^5
Optimal Complexity
Time
O(n)
Space
O(1)
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