Leetcode questions and web link

August 5, 2015

  Here is the table about leetcode questions:

1	Two Sum
2	Add Two Numbers
3	Longest Substring Without Repeating Characters
4	Median of Two Sorted Arrays
5	Longest Palindromic Substring
6	ZigZag Conversion
7	Reverse Integer
8	String to Integer (atoi)
9	Palindrome Number
10	Regular Expression Matching
11	Container With Most Water
12	Integer to Roman
13	Roman to Integer
14	Longest Common Prefix
15	3Sum
16	3Sum Closest
17	Letter Combinations of a Phone Number
18	4Sum
19	Remove Nth Node From End of List
20	Valid Parentheses
21	Merge Two Sorted Lists
22	Generate Parentheses
23	Merge k Sorted Lists
24	Swap Nodes in Pairs
25	Reverse Nodes in k-Group
26	Remove Duplicates from Sorted Array
27	Remove Element
28	Implement strStr()
29	Divide Two Integers
30	Substring with Concatenation of All Words
31	Next Permutation
32	Longest Valid Parentheses
33	Search in Rotated Sorted Array
34	Search for a Range
35	Search Insert Position
36	Valid Sudoku
37	Sudoku Solver
38	Count and Say
39	Combination Sum
40	Combination Sum II
41	First Missing Positive
42	Trapping Rain Water
43	Multiply Strings
44	Wildcard Matching
45	Jump Game II
46	Permutations
47	Permutations II
48	Rotate Image
49	Anagrams
50	Pow(x, n)
51	N-Queens
52	N-Queens II
53	Maximum Subarray
54	Spiral Matrix
55	Jump Game
56	Merge Intervals
57	Insert Interval
58	Length of Last Word
59	Spiral Matrix II
60	Permutation Sequence
61	Rotate List
62	Unique Paths
63	Unique Paths II
64	Minimum Path Sum
65	Valid Number
66	Plus One
67	Add Binary
68	Text Justification
69	Sqrt(x)
70	Climbing Stairs
71	Simplify Path
72	Edit Distance
73	Set Matrix Zeroes
74	Search a 2D Matrix
75	Sort Colors
76	Minimum Window Substring
77	Combinations
78	Subsets
79	Word Search
80	Remove Duplicates from Sorted Array II
81	Search in Rotated Sorted Array II
82	Remove Duplicates from Sorted List II
83	Remove Duplicates from Sorted List
84	Largest Rectangle in Histogram
85	Maximal Rectangle
86	Partition List
87	Scramble String
88	Merge Sorted Array
89	Gray Code
90	Subsets II
91	Decode Ways
92	Reverse Linked List II
93	Restore IP Addresses
94	Binary Tree Inorder Traversal
95	Unique Binary Search Trees II
96	Unique Binary Search Trees
97	Interleaving String
98	Validate Binary Search Tree
99	Recover Binary Search Tree
100	Same Tree
101	Symmetric Tree
102	Binary Tree Level Order Traversal
103	Binary Tree Zigzag Level Order Traversal
104	Maximum Depth of Binary Tree
105	Construct Binary Tree from Preorder and Inorder Traversal
106	Construct Binary Tree from Inorder and Postorder Traversal
107	Binary Tree Level Order Traversal II
108	Convert Sorted Array to Binary Search Tree
109	Convert Sorted List to Binary Search Tree
110	Balanced Binary Tree
111	Minimum Depth of Binary Tree
112	Path Sum
113	Path Sum II
114	Flatten Binary Tree to Linked List
115	Distinct Subsequences
116	Populating Next Right Pointers in Each Node
117	Populating Next Right Pointers in Each Node II
118	Pascal's Triangle
119	Pascal's Triangle II
120	Triangle
121	Best Time to Buy and Sell Stock
122	Best Time to Buy and Sell Stock II
123	Best Time to Buy and Sell Stock III
124	Binary Tree Maximum Path Sum
125	Valid Palindrome
126	Word Ladder II
127	Word Ladder
128	Longest Consecutive Sequence
129	Sum Root to Leaf Numbers
130	Surrounded Regions
131	Palindrome Partitioning
132	Palindrome Partitioning II
133	Clone Graph
134	Gas Station
135	Candy
136	Single Number
137	Single Number II
138	Copy List with Random Pointer
139	Word Break
140	Word Break II
141	Linked List Cycle
142	Linked List Cycle II
143	Reorder List
144	Binary Tree Preorder Traversal
145	Binary Tree Postorder Traversal
146	LRU Cache
147	Insertion Sort List
148	Sort List
149	Max Points on a Line
150	Evaluate Reverse Polish Notation
151	Reverse Words in a String
152	Maximum Product Subarray
153	Find Minimum in Rotated Sorted Array
154	Find Minimum in Rotated Sorted Array II
155	Min Stack
156	Binary Tree Upside Down
157	Read N Characters Given Read4
158	Read N Characters Given Read4 II - Call multiple times
159	Longest Substring with At Most Two Distinct Characters
160	Intersection of Two Linked Lists
161	One Edit Distance
162	Find Peak Element
163	Missing Ranges
164	Maximum Gap
165	Compare Version Numbers
166	Fraction to Recurring Decimal
167	Two Sum II - Input array is sorted
168	Excel Sheet Column Title
169	Majority Element
170	Two Sum III - Data structure design
171	Excel Sheet Column Number
172	Factorial Trailing Zeroes
173	Binary Search Tree Iterator
174	Dungeon Game
179	Largest Number
186	Reverse Words in a String II
187	Repeated DNA Sequences
188	Best Time to Buy and Sell Stock IV
189	Rotate Array
190	Reverse Bits
191	Number of 1 Bits
198	House Robber
199	Binary Tree Right Side View
200	Number of Islands
201	Bitwise AND of Numbers Range
202	Happy Number
203	Remove Linked List Elements
204	Count Primes
205	Isomorphic Strings
206	Reverse Linked List
207	Course Schedule
208	Implement Trie (Prefix Tree)
209	Minimum Size Subarray Sum
210	Course Schedule II
211	Add and Search Word - Data structure design
212	Word Search II
213	House Robber II
214	Shortest Palindrome
215	Kth Largest Element in an Array
216	Combination Sum III
217	Contains Duplicate
218	The Skyline Problem
219	Contains Duplicate II
220	Contains Duplicate III
221	Maximal Square
222	Count Complete Tree Nodes
223	Rectangle Area
224	Basic Calculator
225	Implement Stack using Queues
226	Invert Binary Tree
227	Basic Calculator II
228	Summary Ranges
229	Majority Element II
230	Kth Smallest Element in a BST
231	Power of Two
232	Implement Queue using Stacks
233	Number of Digit One
234	Palindrome Linked List
235	Lowest Common Ancestor of a Binary Search Tree
236	Lowest Common Ancestor of a Binary Tree
237	Delete Node in a Linked List
238	Product of Array Except Self
239	Sliding Window Maximum
240	Search a 2D Matrix II
241	Different Ways to Add Parentheses
242	Valid Anagram
243	Shortest Word Distance
244	Shortest Word Distance II
245	Shortest Word Distance III
246	Strobogrammatic Number
247	Strobogrammatic Number II
248	Strobogrammatic Number III
249	Group Shifted Strings
250	Count Univalue Subtrees
251	Flatten 2D Vector

Leetcode study time

August 2, 2015

在http://zzk.cnblogs.com/　用"找一找",　花了几个小时,　找出比较好的Leetcode博客．

Read the leetcode question and solutions:

1. Find lowest common ancestor in binary tree:

blog of a facebook programmer working on leetcode questions:

递归版本：空间O(1)，时间O(n)

http://www.cnblogs.com/chkkch/archive/2012/11/26/2788795.html

Try it myself and compare to solutions in my blog:
http://juliachencoding.blogspot.ca/2015/07/leetcode-lowest-common-ancestor-in.html

2. Reverse nodes in k group

http://www.cnblogs.com/lichen782/p/leetcode_Reverse_Nodes_in_kGroup.html

http://www.cnblogs.com/grandyang/p/4606710.html


3.  binary tree

http://www.cnblogs.com/wwwjieo0/p/3891037.html

4. All 158 leetcode algorithm implementation in git hub:

http://coolshell.cn/articles/1870.html

Leetcode solution on git hub (use this one more often, best answer, author profile: http://coolshell.cn/haoel)

https://github.com/haoel/leetcode/tree/master/algorithms

5. Leetcode using C#

https://github.com/xisuogu/LeetSharp/tree/master/LeetSharp

6. One more to read



http://blog.csdn.net/u014674776/article/category/2296455

辛苦了几个小时,　总算可以出门放松，打打网球，准备明日爬山了!

Leetcode: lowest common ancestor in binary tree

July 30, 2015

problem statement:

lowest common ancestor in binary tree, question No: 236

Try 4 implementations, 2 passes, but 2 failed. 

read blogs: 

http://articles.leetcode.com/2011/07/lowest-common-ancestor-of-a-binary-tree-part-i.html

http://huangyawu.com/leetcode-lowest-common-ancestor-of-a-binary-tree/

http://www.cnblogs.com/chkkch/archive/2012/11/26/2788795.html

write C# code: 

https://github.com/jianminchen/LowestCommonAncestorInBinaryTree/blob/master/LowestCommonAncestorB.cs

CSS, JavaScript, Jquery learning

July 27, 2015

Basic training code for CSS, html, Jquery, Javascript from books, public internet, and other people's blog. Training basics, know concepts.  

Learning a new language takes time, know syntax, memorize CSS selectors, and then, read "Head first CSS" and understand basic box model, rules, cascading rules, specificity in CSS etc.; she should have stayed more organized.

She tries to learn more about CSS, html, Java Script, practice more code. 

https://github.com/jianminchen/JavaScriptAndPHP

https://github.com/jianminchen/JQueryExamples

https://github.com/jianminchen/CSSExamples

https://github.com/jianminchen/JavaScriptCNBlogs_DolphinX

https://github.com/jianminchen/JQueryExamples

https://github.com/jianminchen/JavaScriptPattern

My favorite thing to do is to challenge myself, try to memorize something over 10 times and see if it will help me learn a new language, improve programming performance. 

Java Script cheat sheet from book Pocket Guide To JavaScript is my favorite one to read, and practice to memorize. 

Here is another one: 

http://www.cheatography.com/davechild/cheat-sheets/javascript/

SQL Server DBA, database design, and development

July 28, 2015

SQL server DBA most popular guidelines for self-learner:

1.       Database may be set up simple transaction log, so the database can be fixed size; never worry about disk space;

2.      Back up database every day; no pressure to work on live database update; certainly, reduce risk to manual update record one by one instead of update statement. 

Also, the website to find the SQL performance script to do daily monitor using database mail setup, so database disk space, backup log, auto growth log, and all other activity can be helpful for every morning.

Here is her favorite site to get the SQL script:

https://ola.hallengren.com/

Never too later to share her thoughts and great ideas with outside world, also her first blog about SQL server DBA experience.

Leetcode Question No 70: climbing stairs

July 28, 2015

Problem statement:

You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

The problem is most popular question in the algorithm, so I do like to spend time to find out all sorts of solution, and get myself comfortable to all kinds of ideas, and figure out which one is best, and all concerns we can have in the discussion of climbing stairs:

1. Recursion solution vs. DP problem solution (Dynamic Programming solution)

2. Time complexity solution: O(2^n) vs O(n) solution

3. The space O(N) vs O(1), in other words: array of N or 2 variable, and another tmp variable

4. The base case discussion: f(0) = 1 or f(0) =1, math question?

5. Math formula - closed form solution vs DP problem solution
6. Use Memoization DP vs. no memoization DP
7. Programming skills, how to make code easy to follow, more readable, more abstract. 

The investment of time on the problem is well done. Go over 16 implementation one by one using C# programming language. 

C# code:

https://github.com/jianminchen/climbingStairs/blob/master/climbingStairs.cs

其实, 我觉得题目越容易, 越值得投入时间去学习; 看看大家有没有不同的理解, 打开思路; 如果自己没有训练过这道题, 可能会紧张; 即使训练过, 但是, 有的想法, 可能自己从来没有思考过, 一时还不能判断好坏, 但是, 多看网上的博客, 向每一个人取取经. 谦虚, 才能有提高.

我编网站后台, C#程序自己写; 自己训练的题目太少; 这次选择用Leetcode来提高C#编程, 又可以提高算法和数据结构的知识, 网站后台靠平时训练.  

January 3, 2016

Review the leetcode question 70, climbing stairs. 

Read the blog:

http://blog.csdn.net/kenden23/article/details/17377869
http://yucoding.blogspot.ca/2012/12/leetcode-question-15-climbing-stairs.html

http://www.cnblogs.com/springfor/p/3886576.html

http://www.cnblogs.com/springfor/p/3886576.html

http://siddontang.gitbooks.io/leetcode-solution/content/dynamic_programming/climbing_stairs.html

https://github.com/zwxxx/LeetCode/blob/master/Climbing_Stairs.cpp

Algorithm reading time

July 26, 2015

 So lucky to come cross the webpages and then start to read, great reading time:

http://www3.cs.stonybrook.edu/~rezaul/Spring-2015/CSE548/Yonghui-Wu/lecture-2-1.pdf

Competitive Programming for Solving Algorithmic Problems:
http://www3.cs.stonybrook.edu/~rezaul/CSE548-S15.html

Leetcode 238: Product of Array except itself

July 24, 2015

 Introduction

I like to share the article talking about Google interview written in Chinese. The article is called "死理性派教你做谷歌面试题", the link is here. 

The experience of working on Leetcode is so challenging. I fully understand the solution but after a few days, I have no clue how it works. But there are so many good articles to read. 

Leetcode 238 in Chinese

  转载上面网页最后一段.

  不同于上面的“流传”，下面两道是已被确认了的google面试题。

第一题，给你一个长度为 N 的链表。N 很大，但你不知道 N 有多大。你的任务是从这 N 个元素中随机取出 k 个元素。你只能遍历这个链表一次，且必须保证取出的元素是完全随机的（出现概率均等）。

第二题，给你一个数组 A [ 1 .. n ] ，请你在 O ( n ) 的时间里构造一个新的数组 B [ 1 .. n ] ，使得 B [ i ] = A [ 1 ] * A [ 2 ] * ... * A [ n ]／A [ i ] 。你不能使用除法运算。

这两道题目看起来很专业，但有趣的是，即使没有学过信息学的人也可以想到答案。

第一题的意思就是有一大串物品，它们能且仅能逐个经过你眼前一次。你不知道它们的个数，要求你从中随机地抽取 k 个物品，同时必须保证取出的元素是完全随机的（出现概率均等）。

第二题给出了一个数列 A [ 1 .. n ] ，要求在较短的时间内不用除法构造一个新数列 B [ 1 .. n ] ，使得 B [i] = A [ 1 ] * A [ 2 ] * ... * A [ n ]／A [ i ] 。 n是这个数组的长度。而 O ( n ) 是评判计算方法速度的标准。如果一个解答方法在n任意变化的情况下，都能满足总共的计算次数相当于是 n 乘以一个常数C这个条件，那么就称这个解答方法是 O ( n ) 的；如果这个解答方法能满足总共的计算次数是 n ² 乘以常数C，那么这个解答方法就被称作是 O ( n ² ) 的。

第一题没有告诉我们物品的个数N，所以我们没法算出 k／N，连最基本的每样物品被选中的概率都不知道，还怎么继续操作呢？既然我们不知道一共有多少个物品，那我们就应该在所有的物品都经过我们眼前之后再做抉择。当每个物品经过我们眼前的时候，可以设法对应地给它生成一个 0 到 1 之间的随机数。等到我们见过了所有的物品之后，只需要选择对应的随机数最大的前 k 个物品就行了。

第二题不允许用除法增加了不少难度。 B [ i ] 不用除法来表示的话就是： B [ i ] = A [ 1 ] * ... * A [ i - 1 ] * A [ i + 1 ] * ... * A [ n ] 。若按照这个表达式进行计算，生成每个 B[ i ] 的时候要进行n - 1次乘法，这样一来完全生成 B [ 1 .. n ] 就需要 O ( n ² ) 的时间了。我们需要通过减少重复的运算来提高效率。

注意到 B [ i ] 可以看作是两个部分的乘积， A [ 1 ] * ... * A [ i - 1 ] 和 A [ i + 1 ] * ... * A [ n ] 。同理 B [ i + 1 ] 就由 A [ 1 ] * ... * A [ i - 1 ] * A [ i ] 和 A [ i + 2 ] * ... * A [ n ] 组成。计算 B [ i ] 时的许多乘法在计算 B [ i + 1 ] 的时候又进行了一遍，因此可以重复利用上一次运算的结果，以避免无谓的运算。从这点出发，我们构造两个新的数列：

S [ i ] = A [ 1 ] * ... * A [ i – 1 ]
T [ i ] = A [ i + 1 ] * ... * A [ n ]

因为生成完整的 S [ 1 .. n ] 和 T [ 1 .. n ] 都能在 O ( n ) 的时间内完成，那么根据 B [ i ] = S [ i ] * T [ i ] 这条式子，生成整个 B [ 1 .. n ] 便也能够在 O ( n ) 的时间内完成了。

不得不说，谷歌是个很爱玩的公司。它曾在MIT校园内到处张贴着一份密码，据说，这份密码包含了一个Google Jobs的电话号码，解开密码的人可以通过此电话留下自己的个人信息，进入谷歌工作。各位读者，你能解开这个密码吗？如果有漂亮的解答，我会在这里贴出来。