📌 LeetCode 100 Days Challenge

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Period 1: Basic Programming (Day 1–10)

#	Problem	Link	Est. Time	Status
1	Two Sum	Link	1h	✅
2	Add Two Numbers	Link	1.5h	☐
3	Reverse Integer	Link	1h	☐
4	Palindrome Number	Link	1h	☐
5	Plus One	Link	1h	☐
6	Sqrt(x)	Link	1h	☐
7	Pow(x, n)	Link	1h	☐
8	Merge Sorted Array	Link	1h	☐
9	Remove Duplicates from Sorted Array	Link	1h	☐
10	Climbing Stairs	Link	1h	☐

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Period 2: Control Structures (Day 11–20)

#	Problem	Link	Est. Time	Status
1	Fizz Buzz	Link	0.25h	☐
2	Roman to Integer	Link	1h	✅
3	Integer to Roman	Link	1.5h	☐
4	String to Integer (atoi)	Link	1.5h	☐
5	Valid Parentheses	Link	1h	☐
6	Implement strStr()	Link	1h	☐
7	Count and Say	Link	1h	☐
8	Longest Common Prefix	Link	1h	☐
9	Length of Last Word	Link	0.5h	☐
10	Add Binary	Link	1h	☐

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Period 3: Strings (Day 21–30)

#	Problem	Link	Est. Time	Status
1	Longest Substring Without Repeating Characters	Link	2h	☐
2	Longest Palindromic Substring	Link	2h	☐
3	Group Anagrams	Link	2h	☐
4	Valid Anagram	Link	1h	☐
5	Minimum Window Substring	Link	2h	☐
6	Valid Palindrome	Link	1h	☐
7	Implement strStr()	Link	1h	☐
8	Count and Say	Link	1h	☐
9	Longest Common Prefix	Link	1h	☐
10	Multiply Strings	Link	2h	☐

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Period 4: Linked Lists (Day 31–40)

#	Problem	Link	Est. Time	Status
1	Merge Two Sorted Lists	Link	1h	☐
2	Remove Nth Node From End of List	Link	1h	☐
3	Reverse Linked List	Link	1h	☐
4	Swap Nodes in Pairs	Link	1h	☐
5	Linked List Cycle	Link	1h	☐
6	Intersection of Two Linked Lists	Link	1h	☐
7	Add Two Numbers II	Link	1.5h	☐
8	Reorder List	Link	1.5h	☐
9	Copy List with Random Pointer	Link	2h	☐
10	Flatten a Multilevel Doubly Linked List	Link	2h	☐

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Period 5: Arrays (Day 41–50)

#	Problem	Link	Est. Time	Status
1	Best Time to Buy and Sell Stock	Link	1h	☐
2	Maximum Subarray	Link	1h	☐
3	Move Zeroes	Link	1h	☐
4	Rotate Array	Link	1h	☐
5	Contains Duplicate	Link	1h	☐
6	Product of Array Except Self	Link	1.5h	☐
7	Merge Intervals	Link	1.5h	☐
8	Insert Interval	Link	1.5h	☐
9	Summary Ranges	Link	1h	☐
10	Spiral Matrix	Link	2h	☐

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Period 6: Trees (Day 51–60)

#	Problem	Link	Est. Time	Status
1	Maximum Depth of Binary Tree	Link	1h	☐
2	Same Tree	Link	1h	☐
3	Symmetric Tree	Link	1h	☐
4	Binary Tree Inorder Traversal	Link	1h	☐
5	Binary Tree Level Order Traversal	Link	1h	☐
6	Convert Sorted Array to Binary Search Tree	Link	1h	☐
7	Path Sum	Link	1h	☐
8	Balanced Binary Tree	Link	1h	☐
9	Minimum Depth of Binary Tree	Link	1h	☐
10	Construct Binary Tree from Preorder and Inorder Traversal	Link	2h	☐

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Period 7: Recursion & Backtracking (Day 61–70)

#	Problem	Link	Est. Time	Status
1	Subsets	Link	1h	☐
2	Subsets II	Link	1.5h	☐
3	Permutations	Link	1.5h	☐
4	Permutations II	Link	1.5h	☐
5	Combinations	Link	1.5h	☐
6	Combination Sum	Link	1.5h	☐
7	Combination Sum II	Link	1.5h	☐
8	Generate Parentheses	Link	2h	☐
9	Word Search	Link	2h	☐
10	N-Queens	Link	3h	☐

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Period 8: Dynamic Programming (Day 71–80)

#	Problem	Link	Est. Time	Status
1	Fibonacci Number	Link	0.5h	☐
2	Coin Change	Link	2h	☐
3	Longest Increasing Subsequence	Link	2h	☐
4	Unique Paths	Link	1.5h	☐
5	Minimum Path Sum	Link	1.5h	☐
6	Climbing Stairs (DP)	Link	1h	☐
7	Edit Distance	Link	3h	☐
8	Maximum Product Subarray	Link	2h	☐
9	House Robber	Link	1.5h	☐
10	House Robber II	Link	2h	☐

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Period 9: Graphs (Day 81–90)

#	Problem	Link	Est. Time	Status
1	Number of Islands	Link	2h	☐
2	Clone Graph	Link	2h	☐
3	Course Schedule	Link	2h	☐
4	Course Schedule II	Link	2h	☐
5	Word Ladder	Link	3h	☐
6	Word Ladder II	Link	3h	☐
7	Graph Valid Tree	Link	2h	☐
8	Pacific Atlantic Water Flow	Link	2h	☐
9	Redundant Connection	Link	2h	☐
10	Surrounded Regions	Link	2h	☐

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Period 10: Advanced Topics (Day 91–100)

#	Problem	Link	Est. Time	Status
1	LRU Cache	Link	2h	☐
2	LFU Cache	Link	3h	☐
3	Median of Two Sorted Arrays	Link	3h	☐
4	Regular Expression Matching	Link	3h	☐
5	Wildcard Matching	Link	3h	☐
6	Trapping Rain Water	Link	2h	☐
7	Minimum Window Substring	Link	2h	☐
8	Sliding Window Maximum	Link	2h	☐
9	Merge k Sorted Lists	Link	3h	☐
10	First Missing Positive	Link	2h	☐