han8909227 / leetcode

Leetcode problems I've been through, with detail problem solving strategy

LeetCode Marathon

To aid my coding skill and to succeed in coding interview I am working on a collection of LeetCode problems.

Goal of this repository

My goal is to help other Python developer who are studying for coding interviews to have a better reference and insight to Leet Code problems, since many of the article/blog on Leet Code problems are written in Java.

Want to contribute?

• First fork it !
• Add problem and your solution to the appropriate classifier folder
• Submit a pull request to this main repository
• Upon review your contribution will be showing in this repo that will help many others!

Further explainations

I have constructed a blog site to post my thought process on solving some of the problems listed below It can be linked to HERE

Solved LeetCode Problems

#	Title	Solution	Time	Space	Notes
2	Add Two Numbers	Python	O(n)	O(1)
13	Roman to Integer	Python	O(n)	O(1)
17	Letter Combinations of a Phone Number	Python	O(n * 4^n)	O(n)
20	Valid Parentheses	Python	O(n)	O(n)
24	Swap Nodes in Pairs	Python	O(n)	O(1)
33	Search in Rotated Sorted Array	Python	O(logn)	O(1)
34	Search for a Range	Python	O(logn)	O(1)
45	Jump Game II	Python	O(n)	O(1)
55	Jump Game	Python	O(n)	O(1)
61	Rotate List	Python	O(n)	O(1)
62	Unique Paths	Python	O(m * n)	O(m + \n)
63	Unique Paths II	Python	O(m * n)	O(m + n)
74	Search a 2D Matrix	Python	O(logm + logn)	O(1)
78	Subsets	Python	O(n * 2^n)	O(1)
92	Reverse Linked List II	Python	O(n)	O(1)
96	Unique Binary Search Trees	Python	O(n)	O(1)
98	Validate Binary Search Tree	Python	O(n)	O(1)
102	Binary Tree Level Order Traversal	Python	O(n)	O(n)
103	Binary Tree Zigzag Level Order Traversal	Python	O(n)	O(n)
111	Minimum Depth of Binary Tree	Python	O(n)	O(h)
112	Path Sum	Python	O(n)	O(h)
113	Path Sum II	Python	O(n)	O(h)	Asked with LC112
116	Populating Next Right Pointers in Each Node	Python	O(n)	O(1)	Asked with LC117
117	Populating Next Right Pointers in Each Node II	Python	O(n)	O(1)	Asked with LC116
121	Best Time to Buy and Sell Stock	Python	O(n)	O(1)	Easy
122	Best Time to Buy and Sell Stock II	Python	O(n)	O(1)
124	Binary Tree Maximum Path Sum	Python	O(n)	O(h)
127	Word Ladder	Python	O(n * d)	O(d)
141	Linked List Cycle	Python	O(n)	O(1)
142	Linked List Cycle II	Python	O(n)	O(1)
150	Evaluate Reverse Polish Notation	Python	O(n)	O(n)
155	Min Stack	Python	O(n)	O(1)
160	Intersection of Two Linked Lists	Python	O(n + m)	O(1)
200	Number of Islands	Python	O(m * n)	O(m * n)	Matrix, LinkedList
206	Reverse Linked List	Python	O(n)	O(1)
232	Implement Queue using Stacks	Python	O(1), amortized	O(n)
236	Lowest Common Ancestor of a Binary Tree	Python	O(n)	O(h)
257	Binary Tree Paths	Python	O(n * h)	O(h)
283	Move Zeroes	Python	O(n)	O(1)
380	Insert Delete GetRandom O(1)	Python	O(1)	O(n)
416	Partition Equal Subset Sum	Python	O(n * s)	O(s)
437	Path Sum III	Python	O(n)	O(h)
449	Serialize and Deserialize BST	Python	O(n)	O(h)
496	Next Greater Element	Python	O(n)	O(1)	Asked with LC503
503	Next Greater Element II	Python	O(n)	O(1)	Asked with LC496
545	Boundary of Binary Tree	Python	O(n)	O(h)
547	Friend Circles	Python	O(n^2)	O(n)	Union Find
746	Min Cost Climbing Stairs	Python	O(n)	O(1)

Clarify questions to ask at interview:

1. Array:

   • Sorted or not?
   • How many elements?
   • Element type? Int, float, double?
   • What's the range of those numbers? Positive or negative?
   • Contain duplicates or not?
   • Subsequence: adjacent or not?

2. Binary tree:

   • Binary search tree or normal binary tree?
   • Balanced or not?
   • Complete or not?
   • Has parent pointer or not?

3. Linked list:

   • Singly or doubly linked list?
   • Has duplicated nodal value or not?

4. String:

   • Need to remove white spaces? Tab and newline?
   • Only has digits? English letters? Upper or lower case?

5. Graph:

   • How many nodes and edges?
   • Directed or undirected?
   • Edges have weights? If so, what's the range?
   • Has loops? Negative sum loops?

6. Return value:

   • What should my method return?
   • If there are multiple solutions to the problem, which one should be returned?
   • If it should return multiple values, do you have any preference on what to return?
   • What should I do/return if the input is invalid / does not match the constraints?