Trapping Rain Water - Leetcode 42 - 2 Pointers (Python)

[@GregHogg]

Master Data Structures & Algorithms For FREE at AlgoMap.io!

[@hlubradio2318]

Hey Greg FYI the more I have been watching your videos for a few weeks now and I can say you're a genuis.

[@GregHogg]

Lololol thank you!!

[@electric336]

This was a great explanation. I did not even think about treating each index as an individual column of water. I was traversing the array to look for valleys, which made the code much more complicated.

[@hlubradio2318]

Actually Greg is beyond all of my college professors.

[@GregHogg]

Awe haha

[@saaddude1]

Thanks for explaining this problem in such an easy way!

[@GregHogg]

Glad to hear it 😊

[@CharlesMurphy1000]

Thanks for the great explanation. Although this is not a two pointer solution, your explanation helped me understand the intuition behind how a two pointer solution works; the one that dynamically keeps track of the left and right max value. Your videos are great, keep them coming!

[@christianjt7018]

Great explanation, you made this hard problem really easy to understand

[@GregHogg]

Oh I'm really happy to hear that

[@dejaphoenix]

These videos that end with "there's a more efficient method but it's pretty complicated" I would love to see a separate video anyway to describe it. Heck, a whole playlist of "the harder way" videos. Or at least a Wikipedia link in the description describing the harder, more efficient algorithm.

[@GregHogg]

Sorry about that!!

[@shivamguys]

Love the way you explain

[@jassemtoumi2876]

Great Explanation !! keep it up

[@khadijaashraf]

awesome visualization! would love to see the O(1) space solution too.

[@NSSanya]

very nice explanation! cheers

[@tanmaysharma3908]

heyy man! great work, i love you!!!

[@venkatamallapu]

if you were not going to show 2 pointers then why did you have it in the title.

[@dharun1510]

Thank man, it is really helpful keep up the Good work. ☺

[@X3Maverick]

Seems like you should take "2 Pointers" out of the video title.

[@GregHogg]

Nah, that's the name of the algorithm

[@X3Maverick]

​@@GregHogg No, this is a 1 pointer solution. The solution you allude to at the end of the video is a 2 pointer solution.

[@MrEmbrance]

this is not 2 pointers approach - this is DP

[@kasmdeliac3264]

why is the title 2 pointer if its not the solution of it?

[@ravi19900]

Test case failed height = [0,1,0,2,1,0,1,3,2,1,2,1] Output - 11 Expected = 6 class Solution(object): def trap(self, height): """ :type height: List[int] :rtype: int """ l_wall = r_wall= 0 n = len(height) max_left = [0] * n max_right = [0] * n for i in range(n): j = -i-1 max_left[i] = l_wall max_right[i] = r_wall l_wall = max(l_wall, height[i]) r_wall = max(r_wall, height[j]) summ = 0 for i in range(n): pot = min(max_left[i] , max_right[i]) summ += max(0, pot - height[i]) return summ

[@malakggh]

Thank you for saying it's stupidity hard 😂😂

[@nandepucharitha9049]

thanks man

[@GregHogg]

My pleasure, thank you so much for your support!

[@anandreddy1976]

class Solution: def trap(self, height: List[int]) -> int: n = len(height) max_L = float('-inf') max_R = float('-inf') L = 0 R = n - 1 count = 0 if n == 0 or n == 1: return 0 while L

[@rahulan9303]

This is not an optimal solution, and you are misguiding

[@AdityaRaj-lj5wf]

this was not two pointers technically

[@MrEmbrance]

it's good solution, but it's not "2 pointers", it's DP

[@GeraudKAMENI]

This is not the best solution, and it's not a two-pointer approach either!!