hard

Trapping Rain Water

Given an elevation map as an array of non-negative bar heights (each of width one), compute how much water is trapped between the bars after rain.

Constraints
  • 1 ≤ n ≤ 2 · 10^4
  • 0 ≤ height[i] ≤ 10^5
Examples
in: height = [0,1,0,2,1,0,1,3,2,1,2,1]
out: 6

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