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						[9/18] 42. Trapping Rain Water
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42. Trapping Rain Water
Hard
22787305Add to ListShareGiven 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.
Example 1:

Input: height = [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6 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.
Example 2:
Input: height = [4,2,0,3,2,5] Output: 9
Constraints:
- n == height.length
- 1 <= n <= 2 * 104
- 0 <= height[i] <= 105
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					Runtime: 207 ms, faster than 54.49% of Python3 online submissions for Trapping Rain Water.
Memory Usage: 16 MB, less than 44.49% of Python3 online submissions for Trapping Rain Water.
				
													
								Memory Usage: 16 MB, less than 44.49% of Python3 online submissions for Trapping Rain Water.
class Solution:
    def trap(self, height: List[int]) -> int:
        l, r = 0, len(height)-1
        
        water = 0
        lmax = rmax = 0
        
        while l <= r:
            lmax, rmax = max(height[l],lmax), max(height[r],rmax)
            if lmax >= rmax:
                
                water += rmax - height[r]
                r -= 1
            else:
                water += lmax - height[l]
                l+=1
        
        return water 
								 
							








