LeetCode

Contains all my Leetcode solutions with Problem statement, their Solutions, Time and Space complexity analaysis.

Graph

#	Title	Difficulty	Remarks
200	Number of Islands	Medium	Done
79	Word Search	Medium	Teaches how to move in all directions of an element in a matrix.
329	Longest Increasing Path in a Matrix	Hard	Done
695	Max Area of Island	Medium	None
130	Surrounded Regions	Medium	None
743	Network Delay Time	Medium	Done :: Dijkstra implementaion with min space utilisation
787	Cheapest Flights Within K Stops	Medium	Time Complexity left
909	Snakes and Ladders	Medium	Done :: Important
785	Is Graph Bipartite?	Medium	Time Complexity left
886	Possible Bipartition	Medium	Time Complexity left
207	Course Schedule	Medium	Done :: Reduced to cycle detection in graph
210	Course Schedule II	Medium	Done
127	Word Ladder	Medium	Revise at the time of interview. Complete BFS application
547	Friend Circles	Medium	DFS implemenation approach is good.Time Complexity left
684	Redundant Connection	Medium	Time Complexity left Kruskal Algorithm

Design

#	Title	Difficulty	Remarks
146	LRU Cache	Medium	Important for interviews
208	Implement Trie (Prefix Tree)	Medium	Time complexity left
211	Add and Search Word	Medium	Time complexity left
380	Insert Delete GetRandom O(1)	Medium	Complexity left

Dynamic Programming

#	Title	Difficulty	Remarks
198	House Robber	Easy	None
746	Min Cost Climbing Stairs	Easy	None
120	Triangle	Medium	None
64	Minimum Path Sum	Medium	None
322	Coin Change	Medium	None
983	Minimum Cost For Tickets	Medium	None
279	Perfect Squares	Medium	None
300	Longest Increasing Subsequence	Medium	None
62	Climbing Stairs	Easy	None
70	Unique Paths	Medium	None
63	Unique Paths II	Medium	None
673	Number of Longest Increasing Subsequence	Medium	None
337	House Robber III	Medium	Different type of DP(Recursion imp.)
72	Edit Distance	Hard	Done :: Classic
368	Largest Divisible Subset	Medium	Done

Back Tracking

#	Title	Difficulty	Remarks
78	Subsets	Medium	Base Concept Problem
90	Subsets II	Medium	Base Concept Problem
46	Permutations	Medium	Base Concept Problem
47	Permutations II	Medium	Base Concept Problem
77	Combinations	Medium	Check if a better approach
17	Letter Combinations of a Phone Number	Medium	None
39	Combination Sum	Medium	None

Tree

#	Title	Difficulty	Remarks
105	Construct Binary Tree from Preorder and Inorder Traversal	Medium	Done :: How to find index quickly
103	Binary Tree Zigzag Level Order Traversal	Medium	None
230	Kth Smallest Element in a BST	Medium	None
116	Populating Next Right Pointers in Each Node	Medium	None
111	Minimum Depth of Binary Tree	Easy	None
112	Path Sum	Easy	BFS and DFS
617	Merge Two Binary Trees	Easy	Time Complexity left
235	LCA of a BST	Easy	Done
236	LCA of a BT	Medium	Done :: Imp
101	Symmetric Tree	Easy	Done :: Imp
98	Validate Binary Search Tree	Medium	Done
104	Maximum Depth of Binary Tree	Easy	Done
108	Convert Sorted Array to BST	Easy	Done :: Imp
102	Binary Tree Level Order Traversal	Medium	Done

Array

#	Title	Difficulty	Remarks
238	Product of Array Except Self	Medium	None
334	Increasing Triplet Subsequence	Medium	None
1305	All Elements in Two Binary Search Trees	Medium	Merger Logic :: Left-Can return list/or not
525	Contiguous Array	Medium	Done
560	Subarray Sum Equals K	Medium	Application of logic same as 525
11	Container With Most Water	Medium	Done
88	Merge Sorted Array	Easy	Done :: No Extra space, trick
1365	How Many Numbers Are Smaller Than the Current Number	Easy	Done :: Trick
42	Trapping Rain Water	Hard	Done :: Classic

Sorting and Searching

#	Title	Difficulty	Remarks
34	Seach for a Range in an array	Medium	Done
33	Search in Rotated Sorted Array	Medium	Done
162	Find Peak Element	Medium	Done :: Left neighbour causes TLE Concept
56	Merge Intervals	Medium	None
986	Interval List Intersections	Medium	Code is Poetry
74	Search a 2D Matrix	Medium	Time Complexity left
240	Search a 2D Matrix II	Medium	Done :: Base concept problem
35	Search Insert Position	Easy	Done
528	Random Pick with Weight	Medium	Done :: IMP

Linked-List

#	Title	Difficulty	Remarks
160	Intersection of Two Linked Lists	Easy	None
142	Linked List Cycle II	Medium	Complexity Left
287	Find the Duplicate Number	Medium	None
141	Linked List Cycle	Easy	Done
138	Copy List with Random Pointer	Medium	Done :: Go through :: See O(1) space solution
237	Delete Node in a Linked List	Easy	Done :: Trick
206	Reverse Linked List	Easy	Done :: Dummy Node
21	Merge Two Sorted Lists	Easy	Done
876	Middle of the Linked List	Easy	Done
2	Add Two Numbers	Medium	Done

Heap

#	Title	Difficulty	Remarks
215	Kth Largest Element in an Array	Medium	Done :: TradeOff
1046	Last Stone Weight	Easy	None
23	Merge k Sorted Lists	Hard	None
621	Task Scheduler	Medium	Pre knowledge required for interviews.

String

#	Title	Difficulty	Remarks
344	Reverse String	Easy	Done
387	First Unique Character in a String	Easy	Done
242	Valid Anagram	Easy	Done
125	Valid Palindrome	Easy	Done :: Regex in java
28	Implement strStr()	Easy	Done :: Break into window size :: Complexity left
38	Count and Say	Easy	Done :: Complexity left
14	Longest Common Prefix	Easy	Done :: Complexity left
443	String Compression	Easy	How the Last index condition is included.
415	Add Strings	Easy	Better code writing. Use of ascii values
1400	Construct K Palindrome Strings	Medium	Good concept of Palindrome

Stack

#	Title	Difficulty	Remarks
443	Asteroid Collision	Medium	Break down the code in smaller cases
496	Next Greater Element I	Medium	Generic implementation of next greater element
1019	Next Greater Node In Linked List	Medium	Done
503	Next Greater Element II	Medium	Done
789	Daily Temperatures	Medium	Done
150	Evaluate Reverse Polish Notation	Medium	Done

Math

#	Title	Difficulty	Remarks
50	Pow(x, n)	Medium	Done :: Logic
172	Factorial Trailing Zeroes	Easy	Done :: Logic
171	Excel Sheet Column Number	Easy	Done

Others

#	Title	Difficulty	Remarks
463	Island Perimeter	Easy	None
844	Backspace String Compare	Easy	None
7	Reverse Integer	Easy	Done :: Overflow condition

30 Day Challenge LeetCode Quarantine-Things

#	Title	Difficulty	Topic	Remarks
136	Single Number	Easy	Math	Done
202	Happy Number	Easy	Math	Time Complexity left
52	Maximum Subarray	Easy	DP	Kadane's algorithm
283	Move Zeroes	Easy	Array	Done
122	Best Time to Buy and Sell Stock II	Easy	Array	Done
49	Group Anagrams	Medium	HashMap/String	Time Complexity left
NA	Counting Elements	Easy	HashMap	Done
844	Backspace String Compare	Easy	2 pointers	Done :: Glance
155	Min Stack	Easy	Design	Done
543	Diameter of Binary Tree	Easy	Done

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