39. Trapping Rain Water

HardTwo Pointers

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

Input: [0,1,0,2,1,0,1,3,2,1,2,1]

Output: 6

Explanation: 6 units of water are trapped.

Constraints

  • n == height.length
  • 1 <= n <= 2 * 10^4
  • 0 <= height[i] <= 10^5
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