15. BFS Level-Order Traversal & Binary Tree Right Side View • Data Structures & Algorithms: Blind 75 & Big Tech Interview Prep • Rishabh Ki Kaksha

Data Structures & Algorithms: Blind 75 & Big Tech Interview Prep › 15. BFS Level-Order Traversal & Binary Tree Right Side View

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Course Syllabus

Module 1: Big-O Asymptotics, Arrays & Sliding Window

01. Time & Space Complexity Masterclass: Big-O, Big-Theta, Big-Omega & Amortized Analysis 02. Arrays & Hashing: Two Sum, Contains Duplicate & Valid Anagram (Hash Table Lookups) 03. Prefix Sum & Kadane's Algorithm (Maximum Subarray Problem in O(N)) 04. Sliding Window Pattern: Fixed vs Dynamic Windows (Best Time to Buy/Sell Stock)

Module 2: Two Pointers & Binary Search Systems

05. Two Pointers Pattern: Valid Palindrome, 3Sum & Container With Most Water 06. Binary Search Foundations: Search in Rotated Sorted Array & Find Minimum 07. Binary Search on Answer Space: Koko Eating Bananas & Capacity to Ship Packages

Module 3: Linked Lists & Fast-Slow Pointer Patterns

08. Singly vs Doubly Linked Lists & In-Place Pointer Manipulation (Reverse Linked List) 09. Fast & Slow Pointer (Floyd's Cycle Detection): Linked List Cycle & Middle Node 10. Merging & Reordering: Merge Two Sorted Lists, Reorder List & Remove Nth Node

Module 4: Stacks, Queues & Monotonic Stack Architecture

11. Stack Fundamentals: Valid Parentheses & Min Stack in O(1) Time 12. Monotonic Stack Pattern: Daily Temperatures & Next Greater Element 13. Hard Stack Coding: Largest Rectangle in Histogram & Trapping Rain Water

Module 5: Trees, Binary Search Trees & DFS/BFS Traversals

14. Binary Tree Architecture: Max Depth, Same Tree & Invert Binary Tree 15. BFS Level-Order Traversal & Binary Tree Right Side View 16. Binary Search Tree (BST) Properties: Validate BST & Lowest Common Ancestor (LCA) 17. Tree Path Sums & Serialize / Deserialize Binary Tree (Hard)

Module 6: Heaps, Priority Queues & Top-K Problems

18. Min Heap & Max Heap Internals: Array Representation & Heapify in O(N) 19. Top-K Elements Pattern: Kth Largest Element in an Array & Top K Frequent Elements 20. Two-Heap Pattern: Find Median from Data Stream (Hard)

Module 7: Graphs, Topological Sort & Shortest Paths (Dijkstra)

21. Graph Representations (Adjacency Matrix vs List) & DFS/BFS Traversal 22. Matrix Graph Traversal: Number of Islands, Max Area of Island & Clone Graph 23. Topological Sort (Kahn's Algorithm): Course Schedule I & II (Cycle Detection) 24. Disjoint Set Union (DSU / Union-Find): Redundant Connection & Number of Connected Components

Module 8: Dynamic Programming, Backtracking & Bit Manipulation

25. Backtracking Pattern: Subsets, Permutations, Combination Sum & Word Search 26. 1D Dynamic Programming: Climbing Stairs, House Robber & Coin Change 27. Longest Increasing Subsequence (LIS): O(N^2) DP vs O(N log N) Patience Sort 28. 2D Dynamic Programming: Unique Paths, Longest Common Subsequence (LCS) & Edit Distance 29. 0/1 Knapsack Pattern & Partition Equal Subset Sum 30. Bit Manipulation Tricks: Number of 1 Bits (Hamming Weight), Counting Bits & Missing Number

Interactive Lesson Studio

# 15. BFS Level-Order Traversal & Binary Tree Right Side View

> DSA Blind 75 Notes by Rishabh - Topic 15

---

### 1. Breadth-First Search (BFS): Level by Level Traversal 🌊

BFS tree ko horizontal layers (Level 0, Level 1, Level 2...) me explore karta hai.  
**Core Data Structure: Queue (FIFO) (`collections.deque`)**

---

### 2. LeetCode #102: Binary Tree Level Order Traversal

```python
from collections import deque

def levelOrder(root: TreeNode | None) -> list[list[int]]:
    if not root: return []
    res = []
    queue = deque([root])
    
    while queue:
        level_size = len(queue) # Freeze current level snapshot!
        current_level = []
        
        for _ in range(level_size):
            node = queue.popleft()
            current_level.append(node.val)
            if node.left: queue.append(node.left)
            if node.right: queue.append(node.right)
            
        res.append(current_level)
        
    return res
```

---

### 3. LeetCode #199: Binary Tree Right Side View

*Trick:* Har level ke BFS traversal me **aakhri element (`current_level[-1]`)** hi right side se visible hota hai!

```python
def rightSideView(root: TreeNode | None) -> list[int]:
    if not root: return []
    res = []
    queue = deque([root])
    
    while queue:
        level_size = len(queue)
        for i in range(level_size):
            node = queue.popleft()
            if i == level_size - 1:
                res.append(node.val) # Last node of this level!
            if node.left: queue.append(node.left)
            if node.right: queue.append(node.right)
            
    return res
```

---

### 4. Master Comparison Matrix

| Traversal Strategy | Data Structure | Best Used For | Space Complexity |
| :--- | :--- | :--- | :--- |
| **DFS (Depth-First)** | Call Stack / Stack | Subtree properties, Path sums, Tree validation | $O(H)$ ($H = \text{Height}$) |
| **BFS (Breadth-First)**| FIFO Queue | Shortest path, Level-by-level stats, Right side view | $O(W)$ ($W = \text{Max Width}$) |

---
**Next Topic:** 16. Binary Search Tree (BST) Properties: Validate BST & Lowest Common Ancestor (LCA)

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