Arrays, Strings, Stack & Binary Search

Perfect — you've already documented your progress really well on core Linked List problems! Here's a continuation post to cover the remaining problems you solved today. You can title this something like:

🔥

Today’s focus was not just solving problems, but refining problem-solving intuition across strings, stacks, and binary search—here’s what I tackled:

1. Length of Last Word

Problem: Return the length of the last word in a given string.
My Approach:

• Traversed from the end to skip trailing spaces.

• Counted until the next space (or beginning) appeared.
  ✅ No need to split or use STL functions like trim.

2. Find Words Containing a Character

Problem: Return indices of words that contain a given character.
My Approach:

• Nested loop to search character in each word.

• Can be optimized using std::string::find instead of full iteration.
  ✅ Focus: Efficient scanning within strings.

3. Max Frequency of Vowels and Consonants

Problem: Find the most frequent vowel and consonant and return their sum.
My Approach:

• Counted letter frequency using a 26-size array.

• Checked for vowels by comparing indexes (a, e, i, o, u).
  ✅ Classic frequency array use case.

4. Jewels and Stones

Problem: Count how many stones are also jewels.
My Approach:

• Iterated stones, used jewels.find() for each char.

• Optimized version could use unordered_set for constant lookup.
  ✅ Practiced brute-force first, then optimized.

5. Valid Parentheses

Problem: Validate if the bracket string is properly balanced.
My Approach:

• Used a stack to store opening brackets.

• Matched and popped on valid closing brackets.
  ✅ Important for practicing stack fundamentals.

6. Implement Stack Using Queue

Problem: Simulate stack operations using queues only.
My Approach (1-Queue):

• Pushed elements and rotated the queue to maintain order.
  ✅ Smart technique to convert FIFO to LIFO.

7. Guess Number Higher or Lower

Problem: Guess the picked number using limited API.
My Approach:

• Classic binary search to minimize queries.
  ✅ Clean log(n) solution using s + (e - s) / 2 to avoid overflow.

8. Largest Odd Number in String

Problem: Return the largest-valued odd substring.
My Approach:

• Scanned from right to find first odd digit.

• Returned substring up to that index.
  ✅ Handled char-to-int conversion carefully.

9. Longest Common Prefix

Problem: Return the common prefix string from an array of strings.
My Approach:

• Used the first string as a base and shrunk it while comparing.
  ✅ Saves time instead of character-by-character brute-force.

🔚 What I Learned Today:

✅ Writing clean string traversal logic
✅ Mastering stack-based problems
✅ Building real confidence in binary search
✅ Optimizing code by identifying repeated patterns
✅ Better understanding of input constraints for performance

📅 Continuing the Grind
Up next:

Binary Search Deepe Down