|16| [315. Count of Smaller Numbers After Self](https://leetcode.com/problems/count-of-smaller-numbers-after-self/)| [Python](leetcode.com/python/315_Count_of_Smaller_Numbers_After_Self.py)| [Article 1](https://leetcode.com/problems/count-of-smaller-numbers-after-self/discuss/76657/3-ways-(Segment-Tree-Binary-Indexed-Tree-Binary-Search-Tree)-clean-python-code), [Article 2](https://medium.com/@timtim305/leetcode-315-count-of-smaller-numbers-after-self-be529cdfe148), [Vid 1](https://www.youtube.com/watch?v=CWDQJGaN1gY), [Vid 2](https://www.youtube.com/watch?v=ZBHKZF5w4YU) | Hard (Very) | 📌 It's a very hard and advanced problem and need to check again. But before that, learn more on [Binary Indexed Tree](https://www.youtube.com/watch?v=CWDQJGaN1gY), [Segment Tree](https://www.youtube.com/watch?v=ZBHKZF5w4YU), Self-Balancing Trees like [AVL-Tree](https://www.educative.io/courses/data-structures-in-python-an-interview-refresher/JYlwQZmN7V9) and [Red-Black Tree](https://www.educative.io/courses/data-structures-in-python-an-interview-refresher/YQy7Zlz1mEO) also on Bit Manipulation |

|01| [200. Number of Islands](https://leetcode.com/problems/number-of-islands/)| [Python](leetcode.com/python/200_Number_of_Islands.py)|

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