Day 20 Journey: Understanding Binary Trees and Linked Lists

Today's session focused on Binary Trees, and I solved a few Linked List problems. While Linked Lists felt smooth, I need to strengthen my BFS, DFS, and tree traversal strategies.

---

📌 Problems Solved Today

1️⃣ Invert Binary Tree (✅ Easy)

👉 Problem: Given a binary tree, invert it (swap left and right children at every node).
🔹 Approach: Used a recursive DFS approach to swap left and right subtrees at each node. An iterative BFS approach using a queue also works.

2️⃣ Maximum Depth of Binary Tree (✅ Easy)

👉 Problem: Find the maximum depth (height) of a binary tree.
🔹 Approach: Used DFS recursion to calculate the depth of left and right subtrees and took the maximum. An iterative BFS approach using level-order traversal also works.

3️⃣ Diameter of Binary Tree (✅ Easy)

👉 Problem: Find the longest path between any two nodes in a binary tree.
🔹 Approach: Used DFS recursion to compute the depth of subtrees and maintain a global variable to track the longest path.

4️⃣ Balanced Binary Tree (✅ Easy)

👉 Problem: Check if a binary tree is height-balanced (i.e., the depth of left and right subtrees never differs by more than 1).
🔹 Approach: Used DFS recursion, calculating height and checking balance condition at each node.

5️⃣ Same Tree (✅ Easy)

👉 Problem: Given two binary trees, check if they are identical.
🔹 Approach: Used DFS recursion to compare corresponding nodes of both trees.

6️⃣ Subtree of Another Tree (✅ Easy)

👉 Problem: Check if a given tree is a subtree of another tree.
🔹 Approach: Used DFS recursion, checking if two trees are the same at any node and recursively searching the left and right subtrees.

7️⃣ Lowest Common Ancestor of a Binary Search Tree (✅ Medium)

👉 Problem: Given a BST and two nodes, find their lowest common ancestor.
🔹 Approach: Used iterative BST traversal, moving left or right based on the values of the nodes.

8️⃣ Binary Tree Level Order Traversal (✅ Medium)

👉 Problem: Return a list of values for each level of the binary tree.
🔹 Approach: Used BFS with a queue to traverse level by level.

---

💡 Key Takeaways & Next Steps

✅ Trees & recursion feel intuitive but need to work on BFS/DFS more.
✅ Linked Lists were easier to work with but should focus on more complex problems.
✅ Next, I’ll work on graph traversal techniques and advanced Linked List-based algorithms.

📌 Plan for tomorrow:
🔹 BFS & DFS in graphs
🔹 More Linked List-based problems
🔹 Some Medium/Hard tree problems

So far, so good! 💪 Let's keep it going. 🚀