Leetcode 51: N - Queen problems

January 12, 2016

Encourage myself to write blogs about leetcode questions. The following talk encourages me a lot. 

https://www.youtube.com/watch?v=R22dJ7bn-pU&list=PLgYNPs-V9YFPqcnEvbIy5hFE40BjxMbjw&index=2
Hiring Rockstars by Roger Philby

the person likes to write, and then the person must love to read, and then the person must be very curious and intellectual. 

So, Julia likes to build up a good habit to write, and then, to read, and to be curious, and to be intellectual. 

Julia is working on recursive function design, how to handle N-Queen problems. After 6 months, she totally forgets how to solve the problem; So, she continues to read more blogs about this algorithm. 

Review the algorithm again. The following blog gives a good explanation, help me understand the algorithm better.
 blog1 (Java programming language): 
http://blog.csdn.net/linhuanmars/article/details/20667175

Amazed that a person can work on algorithms problems and finish over 300 questions/year, people love algorithms and they must know the power of algorithms to save time and improve efficiency at work. 

http://buttercola.blogspot.ca/search/label/Leetcode
http://buttercola.blogspot.ca/2014/09/leetcode-n-queens.html
Leetcode 314:
https://github.com/jianminchen/Leetcode_C-/blob/master/BinaryTreeVerticalOrderTraversal_314.java

Julia likes to work on the analysis of the algorithm, this pseudo code in the blog may help her quickly recover, from nervous to get familiar with the algorithm. 

• • 
    
  http://yucoding.blogspot.ca/2013/01/leetcode-question-59-n-queens.html

The following blog is well-written, and Julia should write a similar solution using C#, to express her appreciation of good variables names, good analysis. (Rating: 10 from 1-10) 

https://polythinking.wordpress.com/2013/02/27/leetcoden-queens-i-and-ii/

It is fun to read solutions in C++/Java.

Write another version of N-Queen problem in C# to entertain. 
https://github.com/jianminchen/Leetcode_C-/blob/master/51NQueenProblem_B.cs

Good advice from the blog 1: 基本上大部分NP问题的求解都是用这个方式，比如Sudoku Solver，Combination Sum，Combinations，Permutations，Word Break II，Palindrome Partitioning等，所以只要把这个套路掌握熟练,多练习. 

Feb. 2, 2016 It is also a DFS algorithm. 

Leetcode 37: Sudoku Solver

July 19, 2015

Problem statement:

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

Solution 1: 

Great blog to read:

http://blog.csdn.net/fightforyourdream/article/details/16916985

And then, start to implement the solution using C# code:

https://github.com/jianminchen/sudokuSolver/blob/master/Program.cs

Solution 2: 

Read the blog,
http://blog.csdn.net/linhuanmars/article/details/20748761

and then, implement the solution using c# code:

https://github.com/jianminchen/sudokuSolver/blob/master/Program2.cs

Solution 3: (good workout on C# KeyValuePair class)

and then, convert C++ code to C# code from the blog:
https://github.com/yinlinglin/LeetCode/blob/master/SudokuSolver.h

Excellent code in C++, using class for node on the board. Learn a few things, fun to play with the code

C# code:
https://github.com/jianminchen/sudokuSolver/blob/master/Program3.cs

solution 4:
https://github.com/jianminchen/sudokuSolver/blob/master/Program4.cs
source code from the blog:
https://github.com/xiaoxq/leetcode-cpp/blob/master/src/SudokuSolver.cpp

Solution 5:
read the blog: (Good coding! practice more based on this blog)
https://github.com/zwxxx/LeetCode/blob/master/Sudoku_Solver.cpp

and convert the C++ code to C# code, (great workout on C# LinkedList for blank nodes)

https://github.com/jianminchen/sudokuSolver/blob/master/Program5.cs

Solution 6:
read the blog:
http://shanjiaxin.blogspot.ca/2014/04/sudoku-solver-leetcode.html

and convert Java code to C# code, great workout on C# and logic checking "return false"

https://github.com/jianminchen/sudokuSolver/blob/master/Program6.cs

Solution 7:
blog:
http://www.jiuzhang.com/solutions/sudoku-solver/
C# code:
https://github.com/jianminchen/sudokuSolver/blob/master/Program7.cs

Solution 8:
Thanks for the blog's highlight line of code on back tracking; finally, I got it! My logic thinking has flaws on back tracking; extra backtracking is not a good. Minimize the back tracking, only do it when "return false". It makes sense to do that.

blog:
http://bangbingsyb.blogspot.ca/2014/11/leetcode-valid-sudoku-sudoku-solver.html
C# code:
https://github.com/jianminchen/sudokuSolver/blob/master/Program8.cs

Solution 9:
blog:
http://www.cnblogs.com/TenosDoIt/p/3800485.html

C# code:
https://github.com/jianminchen/sudokuSolver/blob/master/Program9.cs

Solution 10:
blog: (Excellent implementation! no extra line or number in the code! Best for memorization! Go through other solutions later. )
https://github.com/rffffffff007/leetcode/blob/master/Sudoku%20Solver.java

C# code:
https://github.com/jianminchen/sudokuSolver/blob/master/Program10.cs

算法理解了, 代码可以记住了; 开始看不同的题解, 看看高手的代码; 从不同的题解中, 模仿模仿! 像打网球, 多接触不同的打法, 开阔眼界; 接着看这道题的题解. 试着从不同角度看一个问题, 多练习改代码; 看自己能不能有自己的看法, 去尝试一点更改, 玩一点花样; 增加练习C#编程的机会.

Also, the code written has been work on readability, learned through my favorite book reading:
http://shop.oreilly.com/product/9780596802301.do

Those favorite rules I like to learn, pick up and follow:
Big fan of DRY (Do not repeat yourself) principle, do one thing a time, break giant expression, using explaining variable or summary variable, and abstract the thing to a function, extract a subproblem to a function. The code is also modified to fit into short memory, less mental baggage to read through. 



Read solutions:

https://github.com/jordandong/myleetcodes/blob/master/SudokuSolver.cpp

https://github.com/Sayericplz/myleetcode/blob/master/isValidSudoku.cpp


BFS, using queue - try to convert it to C#
http://yucoding.blogspot.ca/2013/12/leetcode-question-sudoku-solver.html