feat: populate note files with problem descriptions and code stubs

Add populate-notes.mjs that fetches problem descriptions and
Python/C++ code stubs from LeetCode's GraphQL API. Populated
all 197 NeetCode 150 note files with:
- Problem description (examples, constraints)
- Python code stub (function signature)
- C++ code stub (function signature + includes)

API responses cached in leetcode/.cache/leetcode/ for instant re-runs.

org/study_deck_02/dsa/stack/0726-number-of-atoms.org

@@ -1,18 +1,82 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0726. Number of Atoms :hard:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0726. Number of Atoms][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0726. Number of Atoms][0726. Number of Atoms]]
 :END:
 
+Given a string ~formula~ representing a chemical formula, return /the count of each atom/.
+
+The atomic element always starts with an uppercase character, then zero or more lowercase letters, representing the name.
+
+One or more digits representing that element's count may follow if the count is greater than ~1~. If the count is ~1~, no digits will follow.
+
+ - For example, ~"H2O"~ and ~"H2O2"~ are possible, but ~"H1O2"~ is impossible.
+
+Two formulas are concatenated together to produce another formula.
+
+ - For example, ~"H2O2He3Mg4"~ is also a formula.
+
+A formula placed in parentheses, and a count (optionally added) is also a formula.
+
+ - For example, ~"(H2O2)"~ and ~"(H2O2)3"~ are formulas.
+
+Return the count of all elements as a string in the following form: the first name (in sorted order), followed by its count (if that count is more than ~1~), followed by the second name (in sorted order), followed by its count (if that count is more than ~1~), and so on.
+
+The test cases are generated so that all the values in the output fit in a *32-bit* integer.
+
+*Example 1:*
+
+
+#+begin_src
+Input: formula = "H2O"
+Output: "H2O"
+Explanation: The count of elements are {'H': 2, 'O': 1}.
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: formula = "Mg(OH)2"
+Output: "H2MgO2"
+Explanation: The count of elements are {'H': 2, 'Mg': 1, 'O': 2}.
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: formula = "K4(ON(SO3)2)2"
+Output: "K4N2O14S4"
+Explanation: The count of elements are {'K': 4, 'N': 2, 'O': 14, 'S': 4}.
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= formula.length <= 1000~
+
+ - ~formula~ consists of English letters, digits, ~'('~, and ~')'~.
+
+ - ~formula~ is always valid.
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def countOfAtoms(self, formula: str) -> str:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    string countOfAtoms(string formula) {
+        
+    }
+};
 #+end_src