🚀 LeetCode Top Interview 150 - 150-Day Challenge

Goal: Solve 1 problem daily from the LeetCode Top Interview 150 list to master coding interview patterns.

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📌 Challenge Overview

Metric	Value
🧠 Total Problems	150
🎯 Daily Target	1 problem/day
🗓️ Timeframe	150 days

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📊 Progress Tracker

✅ Solved: 43/150 (29%)

⏳ Remaining: 107/150

📅 Current Streak: 43 days

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📅 Daily Log

Day	Problem No.	Difficulty	Solution	Approach	Time/Space
1	88. Merge Sorted Array	Easy	Code	Three‑pointer reverse merge	O(m+n) / O(1)
2	27. Remove Element	Easy	Code	Forward overwrite valid elements	O(n) / O(1)
3	26. Remove Duplicates from Sorted Array	Easy	Code	Two‑pointer overwrite unique values	O(n) / O(1)
4	80. Remove Duplicates from Sorted Array II	Medium	Code	Two‑pointer limit to 2 occurrences	O(n) / O(1)
5	169. Majority Element	Easy	Code	Boyer‑Moore Voting Algorithm	O(n) / O(1)
6	189. Rotate Array	Medium	Code	Reverse entire + parts to rotate	O(n) / O(1)
7	121. Best Time to Buy and Sell Stock	Easy	Code	Track min price + max profit	O(n) / O(1)
8	122. Best Time to Buy and Sell Stock II	Medium	Code	Greedy or DP (buy low, sell high)	O(n) / O(1) or O(n)
9	55. Jump Game	Medium	Code	Greedy (max reachable index)	O(n) / O(1)
10	45. Jump Game II	Medium	Code	Greedy (range end triggers jump)	O(n) / O(1)
11	274. H-Index	Medium	Code	Sort & binary search	O(n log n) / O(1)
12	380. Insert Delete GetRandom O(1)	Medium	Code	HashMap + ArrayList	O(1) avg / O(n)
13	238. Product of Array Except Self	Medium	Code	Prefix × suffix pass	O(n) / O(1)
14	134. Gas Station	Medium	Code	Greedy reset when tank < 0	O(n) / O(1)
15	135. Candy	Hard	Code	Two‑pass greedy on ratings	O(n) / O(n)
16	42. Trapping Rain Water	Hard	Code	Prefix‑suffix max arrays (or two‑pointer)	O(n) / O(n)
17	13. Roman to Integer	Easy	Code	Right-to-left subtraction logic	O(n) / O(1)
18	12. Integer to Roman	Medium	Code	Greedy subtract + symbol map	O(1) / O(1)
19	58. Length of Last Word	Easy	Code	Reverse scan + skip spaces	O(n) / O(1)
20	14. Longest Common Prefix	Easy	Code	Vertical scan	O(m*n) / O(1)
21	151. Reverse Words in a String	Medium	Code	Two-pointer reverse traversal + trimming	O(n) / O(n)
22	6. Zigzag Conversion	Medium	Code	Simulate zigzag filling rows	O(n) / O(n)
23	28. Find the Index of the First Occurrence in a String	Easy	Code	Java indexOf() or manual match	O(n * m) / O(1)
24	68. Text Justification	Hard	Code	Greedy line packing + space distribution	O(n) / O(1)
25	125. Valid Palindrome	Easy	Code	Two-pointer with character filtering	O(n) / O(1)
26	392. Is Subsequence	Easy	Code	Two-pointer character match	O(n) / O(1)
27	167. Two Sum II - Input Array Is Sorted	Medium	Code	Two-pointer from both ends	O(n) / O(1)
28	11. Container With Most Water	Medium	Code	Two-pointer maximize area	O(n) / O(1)
29	15. 3Sum	Medium	Code	Sort + Two-pointer + Skip duplicates	O(n²) / O(log n) or O(n)
30	209. Minimum Size Subarray Sum	Medium	Code	Sliding window (expand/shrink window)	O(n) / O(1)
31	3. Longest Substring Without Repeating Characters	Medium	Code	Sliding window + HashSet	O(n) / O(min(n, m))
32	30. Substring with Concatenation of All Words	Hard	Code	Sliding window with hashmap	O(n * k) / O(n + k)
33	76. Minimum Window Substring	Hard	Code	Sliding window + counter map	O(n) / O(k)
34	36. Valid Sudoku	Medium	Code	Set validation per row/col/box	O(1) / O(1)
35	54. Spiral Matrix	Medium	Code	Layer-by-layer traversal	O(m*n) / O(1)
36	48. Rotate Image	Medium	Code	Transpose + reverse rows	O(n²) / O(1)
37	73. Set Matrix Zeroes	Medium	Code	Mark first row/col as zero flags	O(m*n) / O(1)
38	289. Game of Life	Medium	Code	In-place state encoding	O(m*n) / O(1)
39	383. Ransom Note	Easy	Code	Char count comparison	O(n) / O(1)
40	205. Isomorphic Strings	Easy	Code	HashMap mapping both directions	O(n) / O(1)
41	290. Word Pattern	Easy	Code	HashMap + split and compare	O(n) / O(1)
42	242. Valid Anagram	Easy	Code	Count chars with array	O(n) / O(1)
43	49. Group Anagrams	Medium	Code	HashMap with sorted key or char count	O(n k log k) / O(n k)

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📈 Progress Visualization

Progress: 🟩🟩🟩🟩 (43/150)

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🛠 How to Use This Repo

• 📁 Each problem has its own folder: Question {Day}/Solution.java
• 🧠 Includes commented explanations and efficient approaches
• 🔄 Solutions use Java, with consistent formatting and naming

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🌟 Upcoming Goals

• ✅ Reach 30 problems by the end of the month
• 📦 Add unit tests for each Java file
• 🔁 Revisit and optimize any early solutions if needed

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