DSA - 1 new, 3 revision (Matrix, DFS, Sliding Window, Binary Search)

Tackled a mix of new challenges and critical revisions, focusing on the philosophy that core patterns—Arrays, Strings, and DFS—must become second nature.

48. Rotate Image (Medium)

Approach

1. Transpose matrix → swap (i, j) with (j, i)
2. Reverse each row

Reflection

• Came up with a half-baked approach
• Missed the transpose + reverse pattern
• Made silly mistakes:
  • Incorrect transpose logic (didn’t limit swaps correctly)
  • Reverse logic not optimized (can use 2-pointer technique → O(n))
• Need to slow down and think clearly before coding

Revisions

297. Serialize and Deserialize Binary Tree (Hard)

Approach

• Use DFS traversal
• Serialize:
  • Store values using delimiter ","
  • Use "N" for null nodes
• Deserialize:
  • Rebuild using DFS
  • Maintain pointer/index across recursion

Reflection

• Solved in <25 mins
• Minor confusion:
  • Pointer increment in deserialization
  • Must pass pointer by reference
  • Avoid loops; rely purely on DFS flow

3. Longest Substring Without Repeating Characters (Medium)

Approach

• Sliding Window + Two Pointers
  • Expand window when valid
  • Shrink when duplicate found
• Use Set / HashMap for tracking characters

Reflection

• Felt easy this time
• Stayed calm and executed step-by-step
• No unnecessary panic → big improvement

33. Search in Rotated Sorted Array (Medium)

Approach

• Modified Binary Search
• Identify sorted half and move accordingly

Reflection

• Took time to internalize edge/else cases
• Once understood → logic felt clear
• Key idea: always move towards the sorted side

🧩 Insights / Learnings

• Core topics must become muscle memory:

  • Array
  • String
  • Binary Search
  • Sorting
  • DFS / BFS

• No excuses for:

  • Array manipulation mistakes
  • Basic data handling errors

• Think like learning math as a kid:

  • Repetition → clarity → speed

• Core methodologies should feel almost memorized

• Data manipulation (arrays, hashmaps, strings):

  • Should be second nature
  • No struggle during implementation

🎯 Closing Thought

“Know your tools so well that thinking becomes optional and execution becomes automatic.”