Daily LeetCode & DSA Journey

A dedicated repository tracking my daily Data Structures & Algorithms practice, problem-solving intuition, and runtime analysis. Synced directly from LeetCode.

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Goals & Practice Strategy

• Consistency: 1+ problem solved daily.
• Complexity First: Analyze time and space complexity before coding; optimize from brute force to optimal patterns.
• Pattern Mastery: Focus on core paradigms: Prefix/Suffix Products, Hash Maps, Two Pointers, Sliding Window, Monotonic Stacks, and Trees.

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Solved Problems Index

Day	#	Problem	Topic	Difficulty	Optimal Approach	Time	Space
01	0217	Contains Duplicate	Arrays & Hashing	Easy	Hash Set Membership	$O(N)$	$O(N)$
02	0242	Valid Anagram	Arrays & Hashing	Easy	Frequency Array / Map	$O(N)$	$O(1)$
03	0001	Two Sum	Arrays & Hashing	Easy	One-Pass Hash Map	$O(N)$	$O(N)$
04	0049	Group Anagrams	Arrays & Hashing	Medium	Categorize by Sorted Str / Char Count Tuple	$O(N \cdot K \log K)$	$O(N \cdot K)$
05	0347	Top K Frequent Elements	Arrays & Hashing	Medium	Bucket Sort / Min-Heap	$O(N)$	$O(N)$
06	0238	Product of Array Except Self	Arrays & Hashing	Medium	Prefix & Postfix Running Products	$O(N)$	$O(1)^*$
07	0125	Valid Palindrome	Two Pointers	Easy	Two Pointers (Inward Scan with isalnum)	$O(N)$	$O(1)$
08	0167	Two Sum II - Input Array Is Sorted	Two Pointers	Medium	Two Pointers (Converging Left/Right Bounds)	$O(N)$	$O(1)$
09	0344	Reverse String	Two Pointers	Easy	Two Pointers (In-place Swap)	$O(N)$	$O(1)$
10	0283	Move Zeroes	Two Pointers	Easy	Fast & Slow Pointers (In-place Partition)	$O(N)$	$O(1)$
11	0027	Remove Element	Two Pointers	Easy	Fast & Slow Pointers (In-place Overwrite)	$O(N)$	$O(1)$
12	0026	Remove Duplicates from Sorted Array	Two Pointers	Easy	Fast & Slow Pointers (Unique Element Placement)	$O(N)$	$O(1)$
13	0977	Squares of a Sorted Array	Two Pointers	Easy	Two Pointers (Outward-in Absolute Comparison)	$O(N)$	$O(N)^*$
14	0643	Maximum Average Subarray I	Sliding Window	Easy	Fixed-Size Sliding Window	$O(N)$	$O(1)$
15	0209	Minimum Size Subarray Sum	Sliding Window	Medium	Dynamic-Size Sliding Window (Shrinking Bounds)	$O(N)$	$O(1)$
16	0003	Longest Substring Without Repeating Characters	Sliding Window	Medium	Dynamic Sliding Window + Last Seen Index Map	$O(N)$	$O(\min(N, M))$
17	1004	Max Consecutive Ones III	Sliding Window	Medium	Dynamic Sliding Window with Zero Counter ($k$ flips)	$O(N)$	$O(1)$
18	0141	Linked List Cycle	Linked List	Easy	Floyd's Cycle-Finding Algorithm (Tortoise & Hare)	$O(N)$	$O(1)$
19	0142	Linked List Cycle II	Linked List	Medium	Floyd's Cycle-Finding Algorithm + Phase 2 Intersection Scan	$O(N)$	$O(1)$
20	0876	Middle of the Linked List	Linked List	Easy	Fast & Slow Pointers (1x vs 2x Step Traversal)	$O(N)$	$O(1)$
21	0202	Happy Number	Hash Table / Two Pointers	Easy	Floyd's Cycle Detection on Digit Square Sums	$O(\log N)$	$O(1)$

*Note on #238 & #977: The output array does not count as extra space for complexity analysis.

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Repository Organization

Solutions are synced automatically upon receiving an Accepted verdict:

leetcode-solutions/
├── 0217-contains-duplicate/
│   ├── README.md                          # Problem statement & constraints
│   └── contains-duplicate.py              # Accepted implementation
├── 0242-valid-anagram/
│   ├── README.md
│   └── valid-anagram.py
├── 0001-two-sum/
│   ├── README.md
│   └── two-sum.py
├── 0049-group-anagrams/
│   ├── README.md
│   └── group-anagrams.py
├── 0347-top-k-frequent-elements/
│   ├── README.md
│   └── top-k-frequent-elements.py
└── 0238-product-of-array-except-self/
│   ├── README.md
│   └── product-of-array-except-self.py
└── 0125-valid-palindrome/
│   ├── README.md
│   └── valid-palindrome.py
└── 0167-two-sum-ii-input-array-is-sorted/
│   ├── README.md
│   └── two-sum-ii-input-array-is-sorted.py
└── 0344-reverse-string/
│   ├── README.md
│   └── reverse-string.py
└── 0283-move-zeroes/
│   ├── README.md
│   └── move-zeroes.py
└── 0027-remove-element/
│   ├── README.md
│   └── remove-element.py
├── 0026-remove-duplicates-from-sorted-array/
│   ├── README.md
│   └── remove-duplicates-from-sorted-array.py
└── 0977-squares-of-a-sorted-array/
│   ├── README.md
│   └── squares-of-a-sorted-array.py
├── 0643-maximum-average-subarray-i/
│   ├── README.md
│   └── maximum-average-subarray-i.py
└── 0209-minimum-size-subarray-sum/
│   ├── README.md
│   └── minimum-size-subarray-sum.py
├── 0003-longest-substring-without-repeating-characters/
│   ├── README.md
│   └── longest-substring-without-repeating-characters.py
└── 1004-max-consecutive-ones-iii/
│   ├── README.md
│   └── max-consecutive-ones-iii.py
├── 0141-linked-list-cycle/
│   ├── README.md
│   └── linked-list-cycle.py
└── 0142-linked-list-cycle-ii/
│   ├── README.md
│   └── linked-list-cycle-ii.py
├── 0876-middle-of-the-linked-list/
│   ├── README.md
│   └── middle-of-the-linked-list.py
└── 0202-happy-number/
│   ├── README.md
│   └── happy-number.py
└── .gitignore
└── Pattern Cheat Sheet.md
└── README.md

Setup & Tools

Platform: LeetCode

Automation: LeetSync / LeetHub v3 (automatic Git commits upon acceptance)

Primary Language: Python 3