14-Day Coding Challenge Plan ( All codes writed without AI )

Status	Day	Title	Summary (English)
✅	1	Two Sum	Find two numbers in an array that sum to a target (use hashmap for O(1) lookups).
✅	2	Reverse String	Reverse a string in-place using two pointers (O(1) space).
✅	3	Palindrome Number	Check if a number reads the same backward (e.g., 121). Handle negatives.
✅	4	Valid Parentheses	Validate if brackets are correctly nested/closed (use a stack).
✅	5	Merge Two Sorted Lists	Combine two sorted linked lists into one (O(n) time, in-place).
✅	6	Maximum Subarray	Find the contiguous subarray with the largest sum (Kadane’s algorithm).
✅	7	Climbing Stairs	Count distinct ways to climb stairs (1 or 2 steps; Fibonacci pattern).
🔲	8	Binary Search	Search a target in a sorted array (O(log n) time). Handle edge cases.
🔲	9	Linked List Cycle	Detect if a linked list has a cycle (Floyd’s Tortoise and Hare algorithm).
🔲	10	Valid Anagram	Determine if two strings are anagrams (e.g., "listen" vs. "silent").
🔲	11	First Missing Positive	Find the smallest missing positive integer in an array (O(n) time, O(1) space).
🔲	12	Rotate Image	Rotate an N×N matrix 90 degrees clockwise (in-place).
🔲	13	Word Break	Check if a string can be segmented into dictionary words (DP solution).
🔲	14	Longest Increasing Subsequence	Find the length of the longest subsequence (DP or patience sorting).