42. Trapping Rain Water | Popular interview problem Leetcode | Competitive programming | CityCoder

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.
Input: [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6

The above elevation map 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. Thanks Marcos for contributing this image!

[debackerr]

Thanks for the explanation. Case anyone is wondering how to do this in Python, here is my approach:

def trapped_water(heights):
volume_trapped = 0

for i in range(1, len(heights)-1):
max_left = max(heights[:i+1])
max_right =

volume_trapped = volume_trapped + min(max_left, max_right) - heights[i]

return volume_trapped

[shobhitranjan]

Very helpful but you should discuss the optimal approach
O(n) too.

[shubhamrane]

Line 24, you should be careful while subtracting height, ex. [1, 10, 4]
Left = 1
Right = 4
Sum = sum + min(1, 4) - 10 [x]
i.e sum = sum - 9 [x]

[vaishalirockzz]

Please also solve Trapping Rain Water II. Thanks

[sushavinu]

Thank you! The clarity in explanation helped me solve this problem.

[dokodiaries]

thank you for helping me to solve one simple logical error in my code

[ansumandas]

Good for understanding the problem though use 2 pointers for optimal solution.

[abhigyanshrivastava]

You're good bro. Keep it up, best of luck!

[diyakukreja]

You elaborated so well. Thanks for sharing

[khashbatenkhbat]

Thank you sir! U saved someone's GPA!!

[foodandme]

You explained it very well... helpfull for students 👍

[bisatisrilatha]

Tq broo nice explaination in less time 🙏🙏 continue this

[techzoo]

Hi, what camera are you doing to shoot the video? It's a very good video!

[RajanSingh-xrcf]

very helpful __but last 2 test case not passes
memory limit exceeded

[snehal]

Great Video Simple and Easy to understand ! Keep it up bro 👍

[ShubhamKumar-mbsm]

Thanks For giving solution in this short video

[bisatisrilatha]

Bro when to use INT_MIN and INT_MAX??

[jyothiprakashpatnaikuni]

What is the time complexity of this code..
I think it is o(n2)..

[dhruvpatel]

very nice explanation..thank you for this video

[mariokrstevski]

But why does this work? Makes no sense why this would be the solution