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54 lines
1.5 KiB
Plaintext
54 lines
1.5 KiB
Plaintext
---
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title: '42. Trapping Rain Water'
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description: 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
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icon: dot
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topics:
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- { name: "Array", slug: "array" }
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- { name: "Two Pointers", slug: "two-pointers" }
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- { name: "Dynamic Programming", slug: "dynamic-programming" }
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- { name: "Stack", slug: "stack" }
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- { name: "Monotonic Stack", slug: "monotonic-stack" }
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issue: "https://github.com/prdlk/leetcode/issues/211"
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sidebar:
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label: 'Trapping Rain Water'
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badge: 'Hard'
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---
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### Example 1:
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- Input: `height = [0,1,0,2,1,0,1,3,2,1,2,1]`
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- Output: `6`
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- Explanation: The above elevation map (black section) is represented by array `[0,1,0,2,1,0,1,3,2,1,2,1]`. In this case, `6` units of rain water (blue section) are being trapped.
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### Example 2:
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- Input: `height = [4,2,0,3,2,5]`
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- Output: `9`
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### Constraints:
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- `n == height.length`
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- `1 <= n <= 2 * 10^4`
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- `0 <= height[i] <= 10^5`
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## Solution
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```py
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class Solution:
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def trap(self, height: list[int]) -> int:
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left, right = 0, len(height) - 1
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leftMax, rightMax = 0, 0
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total = 0
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while left < right:
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leftMax = max(leftMax, height[left])
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rightMax = max(rightMax, height[right])
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if height[left] < height[right]:
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total += leftMax - height[left]
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left += 1
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else:
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total += rightMax - height[right]
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right -= 1
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return total
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```
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