#+ANKI_DECK: study_deck_02
* TODO 0042. Trapping Rain Water :hard:
:PROPERTIES:
:NEETCODE: [[file:../../roadmap.org::*0042. Trapping Rain Water][0042. Trapping Rain Water]]
:END:

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.

*Example 1:*


#+begin_src
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.
#+end_src


*Example 2:*


#+begin_src
Input: height = [4,2,0,3,2,5]
Output: 9
#+end_src


*Constraints:*

 - ~n == height.length~

 - ~1 <= n <= 2 * 10^{4}~

 - ~0 <= height[i] <= 10^{5}~

** TODO Approach
Write your approach here.

** TODO Python
#+begin_src python :lc-problem 42 :lc-lang python3
class Solution:
    def trap(self, height: List[int]) -> int:
#+end_src

** TODO C++
#+begin_src cpp :lc-problem 42
class Solution {
public:
    int trap(vector<int>& height) {
        
    }
};
#+end_src