Cracking the Coding Interview in Python - Solutions with Explanations

Detailed explanations to the coding interview questions in CTCI. The solutions are written in Python 3.

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Arrays and Strings

|Problem Number | Problem Name | Status| |--- | --- | --- | | 1.1 | Is Unique | Read Solution ✅ | | 1.2 | Check Permutation | Read Solution ✅ | 1.3 | URLify | Read Solution ✅ | 1.4 | Palindrome Permutation | Read Solution ✅ | 1.5 | One Away | Read Solution ✅ | 1.6 | String Compression | Read Solution ✅ | 1.7 | Rotate Matrix | Read Solution ✅ | 1.8 | Zero Matrix | Read Solution ✅ | 1.9 | String Rotation | Read Solution ✅ |

Linked Lists

| Problem Number | Problem Name | Status | | --- | --- | --- | | 2.1 | Remove Dups | Read Solution ✅ | | 2.2 | Return Kth to Last | Read Solution ✅ | | 2.3 | Delete Middle Node | Read Solution ✅ | | 2.4 | Partition | Read Solution ✅ | | 2.5 | Sum List | Read Solution ✅ | | 2.6 | Palindrome | Read Solution ✅ | | 2.7 | Intersection | Read Solution ✅ | | 2.8 | Loop Detection | Read Solution ✅ |

Stacks and Queues

| Problem Number | Problem Name | Status | | --- | --- | --- | | 3.1 | Three In One | Read Solution ✅ | | 3.2 | Stack Min | Read Solution ✅ | | 3.3 | Stack of Plates | Read Solution ✅| | 3.4 | Queue via Stacks | Read Solution ✅ | | 3.5 | Sort Stack | ❌ | | 3.6 | Animal Shelter | ❌ |

Trees and Graphs

| Problem Number | Problem Name | Status | | --- | --- | --- | | 4.1 | Route Between Nodes | ❌ | | 4.2 | Minimal Tree | ❌ | | 4.3 | List of Depths | ❌ | | 4.4 | Check Balanced | ❌ | | 4.5 | Validate BST | ❌ | | 4.6 | Successor | ❌ | | 4.7 | Build Order | ❌ | | 4.8 | First Common Ancestor | ❌ | | 4.9 | BST Sequence | ❌ | | 4.10 | Check Subtree | ❌ | | 4.11 | Random Node | ❌ | | 4.12 | Paths with Sum | ❌ |

Bit Manipulation

| Problem Number | Problem Name | Status | | --- | --- | --- | | 5.1 | Insertion | ❌ | | 5.2 | Binary to String | ❌ | | 5.3 | Flip Bit to Win | ❌ | | 5.4 | Next Number | ❌ | | 5.5 | Debugger | ❌ | | 5.6 | Conversion | ❌ | | 5.7 | Pairwise Swap | ❌ | | 5.8 | Draw Line | ❌ |

Object Oriented Design

| Problem Number | Problem Name | Status | | --- | --- | --- | | 7.1 | Deck of Cards | ❌ | | 7.2 | Call Center | ❌ | | 7.3 | Jukebox | ❌ | | 7.4 | Parking Lot | ❌ | | 7.5 | Online Book Reader | ❌ | | 7.6 | Jigsaw | ❌ | | 7.7 | Chat Server | ❌ | | 7.8 | Othello | ❌ | | 7.9 | Circular Array | ❌ |

Recursion and Dynamic Programming

| Problem Number | Problem Name | Status | | --- | --- | --- | | 8.1 | Triple Step | ❌ | | 8.2 | Robot in a Grid | ❌ | | 8.3 | Magic Index | ❌ | | 8.4 | Power Set | ❌ | | 8.5 | Recursive Multiply | ❌ | | 8.6 | Towers of Hanoi | ❌ | | 8.7 | Permutation without Dups | ❌ | | 8.8 | Permutation with Dups | ❌ | | 8.9 | Parens | ❌ | | 8.10 | Paint Fill | ❌ | | 8.11 | Coins | ❌ | | 8.12 | Eight Queens | ❌ | | 8.13 | Stack of Boxes | ❌ | | 8.14 | Boolean Evaluation | ❌ |

Sorting and Searching

| Problem Number | Problem Name | Status | | --- | --- | --- | | 10.1 | Sorted Merge | ❌ | | 10.2 | Group Anagram | ❌ | | 10.3 | Search in Rotated Array | ❌ | | 10.4 | Sorted Search, No Size | ❌ | | 10.5 | Sparse Search | ❌ | | 10.6 | Sort Big File | ❌ | | 10.7 | Missing Int | ❌ | | 10.8 | Find Duplicates | ❌ | | 10.9 | Sorted Matrix Search | ❌ | | 10.10 | Rank from Stream | ❌ | | 10.11 | Peaks and Valleys | ❌ |

Moderate

| Problem Number | Problem Name | Status | | --- | --- | --- | | 16.1 | Number Swapper | Read Solution ✅ | | 16.2 | Word Frequencies | Read Solution ✅ | | 16.3 | Intersection | ❌ | | 16.4 | Tic Tac Win | ❌ | | 16.5 | Factorial Zeros | ❌ | | 16.6 | Smallest Difference | ❌ | | 16.7 | Number Max | ❌ | | 16.8 | English Int | ❌ | | 16.9 | Operations | ❌ | | 16.10 | Living People | ❌ | | 16.11 | Diving Board | ❌ | | 16.12 | XML Encoding | ❌ | | 16.13 | Bisect Squares | ❌ | | 16.14 | Best Line | ❌ | | 16.15 | Master Mind | ❌ | | 16.16 | Sub Sort | ❌ | | 16.17 | Contiguous Sequence | ❌ | | 16.18 | Pattern Matching | ❌ | | 16.19 | Pond Sizes | ❌ | | 16.20 | T9 | ❌ | | 16.21 | Sum Swap | ❌ | | 16.22 | Langton's Ant | ❌ | | 16.23 | Rand7 from Rand5 | ❌ | | 16.24 | Pairs with Sum | ❌ | | 16.25 | LRU Cache | ❌ | | 16.26 | Calculator| ❌ |

Hard

| Problem Number | Problem Name | Status | | --- | --- | --- | | 17.1 | Add Without Plus | ❌ | | 17.2 | Shuffle | ❌ | | 17.3 | Random Set | ❌ | | 17.4 | Missing Number | ❌ | | 17.5 | Letters and Numbers | ❌ | | 17.6 | Count of 2s | ❌ | | 17.7 | Baby Names | ❌ | | 17.8 | Circus Tower | ❌ | | 17.9 | Kth Multiple | ❌ | | 17.10 | Majority Element | ❌ | | 17.11 | Word Distance | ❌ | | 17.12 | BiNode | ❌ | | 17.13 | Re-Space | ❌ | | 17.14 | Smallest K | ❌ | | 17.15 | Longest Word | ❌ | | 17.16 | The Masseuse | ❌ | | 17.17 | Multi Search | ❌ | | 17.18 | Shortest Supersequence | ❌ | | 17.19 | Missing Two | ❌ | | 17.20 | Continuous Median | ❌ | | 17.21 | Volume of Histogram | ❌ | | 17.22 | Word Transformer | ❌ | | 17.23 | Max Black Square | ❌ | | 17.24 | Max Submatrix | ❌ | | 17.25 | Word Rectangle | ❌ | | 17.26 | Sparse Similarity | ❌ |

If you find this useful, a Github star would be much appreciated!! ⭐ ⭐ ⭐