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All topics›JavaScript›Two pointers

Trapping Rain Water

advancedlayer B4 · Two pointers5 tests

height[i] is the height of a bar of width 1. After it rains, water settles in the dips between bars. Return the total units of water trapped.

  • Water above bar i is min(tallest to its left, tallest to its right) - height[i]
  • Never negative — a bar taller than both walls traps nothing
  • Two pointers get this in O(n) time and O(1) space

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