🧠 Day 6 of My #90DaysOfDSA Challenge: Palindromes and Sliding Windows!

📅 Date: May 26, 2025
🏷️ Tags: DSA, Python, LeetCode, Sliding Window, HashMap

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👋 Hello Devs!

Welcome back to my #90DaysOfDSA journey. On Day 6, I focused on solving problems that involve string pairing and sliding window techniques — both of which are common patterns in coding interviews.

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📌 Problem 1: Longest Palindrome by Concatenating Two Letter Words

🔗 LeetCode 2131

🔍 What I learned:

• Using hashmaps to store frequency of words.

• Forming palindromic structures by smartly pairing words and handling center palindromes like "aa", "gg", etc.

• Only one self-palindrome word is allowed in the middle.

🛠️ Key Concepts:

• HashMap / Counter

• Reversible string logic

• Greedy pairing

💻 My Code:

class Solution:
    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
        left = 0
        total = 0
        min_len = float('inf')

        for right in range(len(nums)):
            total += nums[right]
            while total >= target:
                min_len = min(min_len, right - left + 1)
                total -= nums[left]
                left += 1

        return 0 if min_len == float('inf') else min_len

📁 View this code on GitHub

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📌 Problem 2: Minimum Size Subarray Sum

🔗 LeetCode 209

🔍 What I learned:

• How to use the sliding window pattern effectively to reduce time complexity from O(n²) to O(n).

• Shrinking the window only when the current sum is greater than or equal to the target value.

• Always track the minimum valid subarray length.

🛠️ Key Concepts:

• Sliding Window

• Two Pointers

• Greedy optimization

💻 My Code:

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        hashmap={}
        for i,n in enumerate(nums):
            diff=target-n
            if diff in hashmap:
                return [hashmap[diff],i]
            hashmap[n]=i

📁 View this code on GitHub

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💡 Reflections from Today:

I realized that solving problems efficiently isn't just about getting the right answer — it's about finding patterns that work across many problems. Today’s takeaways:

• Use Counter and [::-1] creatively when dealing with word symmetry.

• Apply the sliding window technique to subarray problems where you're optimizing length or sum.

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🚀 What’s Next?

Tomorrow, I plan to:

• Solve more problems involving two pointers and prefix sums

• Focus on problems tagged medium on LeetCode

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🧵 Follow My Journey:

📌 GitHub: Piyush-Karn/DSA-Problems
🐦 Twitter: @CodeWithPiyush

Thanks for reading! See you on Day 7 👋

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