Tackling LeetCode for Interviews

Introduction

• LeetCode is commonly used in tech interviews, especially for FAANG companies.
• A systematic approach is more effective than solving 1000+ problems.
• Many engineers have succeeded with fewer than 100 problems solved.

Simplifying the Problem

• Break down each problem into simple steps.
• Translate the problem statement:
  • Inputs: Data you are given
  • Operations: Actions needed on inputs
  • Outputs: Desired result
• Manually walk through test cases to understand the problem.
• Ask clarifying questions:
  • Is endWord guaranteed in the list?
  • Are words case sensitive?
• Edge cases to consider:
  • beginWord equals endWord
  • Empty word list

Example: Word Ladder

• Simplify: Change beginWord to endWord by altering one letter at a time using words in wordList.
• Test case: Changing 'hit' to 'cog'.
• Questions:
  • Is endWord in word list?
  • Are words case-sensitive?
• Edge Cases:
  • beginWord equals endWord
  • Empty word list

Steps for Solving Problems

1. Explaining the straightforward solution

• Identify time and space complexities.
• Simplify to discover a better solution.

2. Finding the optimal solution

• Identify data structures and algorithms to use.
• Use constraints to hint at algorithms (e.g., O(log(n)) suggests binary search).
• Familiarity with Big O notation and algorithms required.

Brute Force vs Optimal Solution

• Brute Force for Word Ladder:
  • Generates all possible single-letter transformations.
  • Time and space complexity: O(25L)^N.
• Optimal Approach:
  • Use flowchart to identify algorithms.
  • Recognize it is a graph problem; use BFS as it connects shortest paths and is unweighted.
  • Process for BFS:
    1. Starting node is the starting word, keep track of transformations.
    2. Attempt transformation for each letter.
    3. Check if the new word meets conditions (different, exists in wordList, not seen before).
    4. Add to queue if valid and check if it matches endWord.
  • Simple tweaks to BFS can solve patterns in LeetCode problems.

Debugging

• Types of Errors:
  • Syntax errors: fix from error log.
  • Implementation errors: fix by manual walkthrough or print/debug statements.
• Familiarize with common mistakes.

Conclusion

• Follow the step-by-step approach to solve any LeetCode or interview question.
• Practice data structures and algorithms.
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