feat: added LeetCode problem 1,2

.github/workflows/leetcode_directory_writer.yml

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+# The objective of this GitHub Action is to update the leetcode DIRECTORY.md file (if needed)
+# when doing a git push
+name: leetcode_directory_writer
+on:
+  push:
+    paths:
+      - 'leetcode/src/**.cpp'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-python@v4
+        with:
+          python-version: 3.x
+      - name: Add python dependencies
+        run: |
+          pip install requests
+      - name: Write LeetCode DIRECTORY.md
+        run: |
+          python3 scripts/leetcode_directory_md.py 2>&1 | tee leetcode/DIRECTORY.md
+          git pull || true
+      - name: Commit and push changes
+        uses: stefanzweifel/git-auto-commit-action@v4
+        id: commit-push
+        with:
+          commit_message: 'docs: updating `leetcode/DIRECTORY.md`'
+          branch: 'leetcode-directory-${{ github.sha }}'
+          create_branch: true
+      - name: Creating and merging the PR
+        shell: bash
+        if: steps.commit-push.outputs.changes_detected == 'true'
+        run: |
+          gh pr create --base ${GITHUB_REF##*/} --head leetcode-directory-${{ github.sha }} --title 'docs: updating `leetcode/DIRECTORY.md`' --body 'Updated LeetCode directory (see the diff. for changes).'
+          gh pr merge --admin --merge --subject 'docs: updating `leetcode/DIRECTORY.md' --delete-branch
+        env:
+          GH_TOKEN: ${{ github.token }}

leetcode/README.md

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+# 📚 Contributing 📚
+
+We're glad you're interested in adding C++ LeetCode solutions to the repository.\
+Here we'll be explaining how to contribute to LeetCode solutions properly.
+
+## 💻 Cloning/setting up the project 💻
+
+First off, you'll need to fork the repository [**here**](https://github.com/TheAlgorithms/C-Plus-Plus/fork).\
+Then, you'll need to clone the repository to your local machine.
+
+```bash
+git clone https://github.com/your-username/C-Plus-Plus.git
+```
+
+After that, you'll need to create a new branch for your solution.
+
+```bash
+git checkout -b solution/your-solution-name
+```
+
+## 📝 Adding a new solution 📝
+
+All LeetCode problems can be found [**here**](https://leetcode.com/problemset/all/).\
+If you have a solution to any of these problems (which are not being **repeated**, that's great! Here are the steps:
+
+1. Add a new file in `leetcode/src` with the number of the problem.
+    - For example: if the problem's number is 98, the filename should be `98.cpp`.
+2. Provide a small description of the solution at the top of the file. A function should go below that. For example:
+
+```c
+/**
+ * Return an vector of vector of size returnSize.
+ * The sizes of the vectors are returned as returnColumnSizes vector.
+ * Note: Both returned vector and columnSizes vector must be dynamically allocated, assume caller calls free.
+ */
+```
+
+3. Do not provide a `main` function. Use the required standalone functions instead.
+4. Doxygen documentation isn't used in LeetCode solutions. Simple/small documentation or comments should be fine.
+5. Don't include libraries/headers such as `iostream`. Your file should be the solution to the problem only.
+
+> **Note**
+> There was a requirement to update the `leetcode/DIRECTORY.md` file with details of the solved problem. It's not required anymore. The information about the problem is fetched automatically throughout the LeetCode API.
+
+## 📦 Committing your changes 📦
+
+Once you're done with adding a new LeetCode solution, it's time we make a pull request.
+
+1. First, stage your changes.
+
+```bash
+git add leetcode/src/98.cpp # Use `git add .` to stage all changes.
+```
+
+2. Then, commit your changes.
+
+```bash
+git commit -m "feat: add LeetCode problem 98" -m "Commit description" # Optional
+```
+
+3. Finally, push your changes to your forked repository.
+
+```bash
+git push origin solution/your-solution-name:solution/your-solution-name
+```
+
+4. You're done now! You just have to make a [**pull request**](https://github.com/TheAlgorithms/C-Plus-Plus/compare). 🎉
+
+If you need any help, don't hesitate to ask and join our [**Discord server**](https://the-algorithms.com/discord)! 🙂

leetcode/src/1.cpp

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+/*
+* Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
+* You may assume that each input would have exactly one solution, and you may not use the same element twice.
+*/
+
+class Solution {
+public:
+    std::vector<int> twoSum(std::vector<int>& nums, int target) {
+        std::unordered_map<int, int> mp; // value:index
+        std::vector<int> res;
+
+        for (int i = 0; i < nums.size(); i++) {
+            int diff = target - nums[i];
+
+            if (mp.find(diff) != mp.end()) {
+                res.push_back(mp[diff]);
+                res.push_back(i);
+                return res;
+            }
+            mp[nums[i]] = i;
+        }
+        return res;
+    }
+};

leetcode/src/2.cpp

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+/* You are given two non - empty linked lists representing two non - negative integers.
+* The digits are stored in reverse order, and each of their nodes contains a single digit.
+* Add the two numbersand return the sum as a linked list.
+*/
+
+/*
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
+        int carry = 0;
+        ListNode head;
+        ListNode* sum = &head;
+
+        while (l1 || l2) {
+            int val = carry + (l1 ? l1->val : 0) + (l2 ? l2->val : 0);
+            carry = val / 10;
+            sum->next = new ListNode(val % 10);
+            sum = sum->next;
+            l1 = (l1 ? l1->next : nullptr);
+            l2 = (l2 ? l2->next : nullptr);
+        }
+        if (carry) {
+            sum->next = new ListNode(carry);
+        }
+
+        return head.next;
+    }
+};

scripts/leetcode_directory_md.py

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+#!/usr/bin/env python3
+
+from dataclasses import dataclass
+from os import listdir
+from pathlib import Path
+
+import requests
+
+
+@dataclass
+class Task:
+    """The task dataclass. Container for task info"""
+
+    id: str
+    title: str
+    solution: str
+    difficulty: str
+
+
+def fetch_leetcode_folder_tasks(solutions_folder: Path) -> list[Task]:
+    """Fetch leetcode tasks from the Leetcode"""
+
+    # Fetch tasks info from the leetcode API.
+    resp = requests.get("https://leetcode.com/api/problems/algorithms/", timeout=10)
+    content_dict = resp.json()
+
+    raw_tasks_id_dict = {}
+
+    for task in content_dict["stat_status_pairs"]:
+        task_stat = task["stat"]
+        raw_tasks_id_dict[str(task_stat["frontend_question_id"])] = task
+
+    # Generate result tasks info to be inserted into the document
+    tasks_list = []
+
+    difficulty = {1: "Easy", 2: "Medium", 3: "Hard"}
+
+    for fl in listdir(solutions_folder):
+        task_id = fl.split(".")[0]
+
+        raw_task = raw_tasks_id_dict.get(task_id, None)
+        if raw_task is None:
+            continue
+
+        raw_task_stat = raw_task["stat"]
+        tasks_list.append(
+            Task(
+                id=f'{raw_task_stat["frontend_question_id"]}',
+                title=f'[{raw_task_stat["question__title"]}](https://leetcode.com/problems/{raw_task_stat["question__title_slug"]})',
+                solution=f"[C++](./src/{fl})",
+                difficulty=f'{difficulty.get(raw_task["difficulty"]["level"], "")}',
+            )
+        )
+
+    return tasks_list
+
+
+HEADER_ID = "#"
+HEADER_TITLE = "Title"
+HEADER_SOLUTION = "Solution"
+HEADER_DIFFICULTY = "Difficulty"
+SEPARATOR = "-"
+
+
+def print_directory_md(tasks_list: list[Task]) -> None:
+    """Print tasks into the stdout"""
+
+    def get_max_len(get_item):
+        return max(list(map(lambda x: len(get_item(x)), tasks_list)))
+
+    id_max_length = max(get_max_len(lambda x: x.id), len(HEADER_ID))
+    title_max_length = max(get_max_len(lambda x: x.title), len(HEADER_TITLE))
+    solution_max_length = max(get_max_len(lambda x: x.solution), len(HEADER_SOLUTION))
+    difficulty_max_length = max(
+        get_max_len(lambda x: x.difficulty), len(HEADER_DIFFICULTY)
+    )
+
+    def formatted_string(header, title, solution, difficulty):
+        return (
+            f"| {header.rjust(id_max_length)} "
+            + f"| {title.ljust(title_max_length)} "
+            + f"| {solution.ljust(solution_max_length)} "
+            + f"| {difficulty.ljust(difficulty_max_length)} |"
+        )
+
+    tasks_rows = []
+
+    tasks_rows.append(
+        formatted_string(HEADER_ID, HEADER_TITLE, HEADER_SOLUTION, HEADER_DIFFICULTY)
+    )
+    tasks_rows.append(
+        formatted_string(
+            id_max_length * SEPARATOR,
+            title_max_length * SEPARATOR,
+            solution_max_length * SEPARATOR,
+            difficulty_max_length * SEPARATOR,
+        )
+    )
+
+    tasks_list.sort(key=lambda x: int(x.id.strip()))
+
+    for task in tasks_list:
+        tasks_rows.append(
+            formatted_string(task.id, task.title, task.solution, task.difficulty)
+        )
+
+    print(
+        """
+# LeetCode
+
+### LeetCode Algorithm
+"""
+    )
+
+    for item in tasks_rows:
+        print(item)
+
+
+if __name__ == "__main__":
+    top_dir = Path(".")
+    solutions_folder = top_dir / "leetcode" / "src"
+
+    tasks_list = fetch_leetcode_folder_tasks(solutions_folder)
+    print_directory_md(tasks_list)