Trapping Rain Water

Hard~30 min

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
Explanation: The elevation map traps 6 units of rain water.
Example 2
Input: height = [4,2,0,3,2,5]
Output: 9
Explanation: The elevation map traps 9 units of rain water.

Constraints

  • n == height.length
  • 1 <= n <= 2 * 10^4
  • 0 <= height[i] <= 10^5
  • Expected time complexity: O(n)
Code
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Output

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