Leetcode 151: reverse words in a string

May 24, 2017

Problem statement is here.

C# practice is here. Need to work on failed test cases, multiple space, "a   b" should be reversed to "b   a".

Follow up 

April 16, 2017
Mocking experience, reverse words in a string, C# code is here.

June 20, 2017
Mocking experience, reverse words in a string, C# code is here.

Julia learned the lesson how to work on linear scan array hard lesson through Leetcode contest in May, she spent over 40 minutes on one algorithm, and then she read the idea to spend 5 minutes less to write very clear solution. The blog is called Leetcode 605: Can plant flower.

Leetcode 37: Sudoku Solver

May 23, 2017

Introduction

Sudoku solver is the most classical algorithm to apply Depth First Search (DFS) using recursion and also use back tracking as well. Julia had a very good experience in May 22, 2017, she had chance to learn to write a short version of depth first search coached by her mocking peer.

Most important design is about base case. To make the implementation as simple as possible, DFS algorithm can start from the matrix left top corner, and then scan from left to right, top to bottom, if the row is bigger than 8, then it finds a solution.

Algorithm Study 

Problem statement is here.

The C# code practice is here.

Algorithm talk 

May 25, 2017

It is also very good experience to use Sudoku Solver algorithm to conduct mocking experience. Julia did her first mocking experience using the algorithm as an interviewer.

June 13, 2017

It is very good experience to write sudoku in mocking experience, this is the third time Julia worked on Sudoku for mocking experience.

Julia put the code into Visual Studio to compile and here is her C# practice code.

Here are two mistakes in writing through mocking experience:

One compiler error in mocking writing, line 61,
add type conversion by adding (char), and also (number + '0')

line 61  board[row, col] = (char)(number + '0'); // add '0'

One compiler error, duplicate variable inside for loop on line 82, change col to column; line 91, row is changed to rowIndex.

Try to pass online judge, and then find the bug on line 84, 93, 111. C# code is here.

line 84 if (board[row, column] - number == '0') // should be '0', not 0

Actionable Item

Julia still remembered that she got some great advice on her second mocking experience using Sudoku, and then she was coached by the peer to use DFS starting from (0, 0) and set the base case to row > 8.

Leetcode 18: 4 sum

April 6, 2017

Introduction

Julia learned through the mocking experience of the algorithm. 4 sum algorithm optimal time can be lowered to O(N²), not O(N³), not brute force O(N⁴). Although it takes O(N²) space to build a hashtable to store all possible pair of two numbers in the array with the sum and two index of numbers, the algorithm actually beats O(N³).

It is Leetcode 18, Julia learned from the mocking experience. She did not follow the hints at the beginning, she wrote a 3 sum algorithm, which takes O(N²)time; but when she tried to put all possible 3 sum into hashtable, then time complexity will go up to O(N³⁾.

A few things she learned from mocking experience:

1. Stay calm, write down everything slowly. There is a lot of time if it takes slow.
2. First 10 minutes it can be good brainstorm.
3. Try to find the optimal algorithm, take first 5 minutes to think about by yourself first, do not say anything until you are sure about the optimal solution
4. Keep the first 5 minutes private as long as you are not cheating, until you have to say something.

Values of the mocking experience 

Julia did not continue to practice mocking experience when she did not fully experience what she should work on. She stopped at the end of March 2016 with 8 mocking experiences. She guessed that she moved on to practice more on hackerrank coding online test.

The statistics shows that 15 mocking experience will be at least. It is not easy to get those 15 mocking experience. So far, Julia only had 2 times experience starting this April 1. She still has 5 mocking experience to go before she reaches 15.

She understood that she has to focus on problem solving, do not pay too much attention to the partner. But she needs to respond everything he/ she says.

Julia can write better maintainable, readable and clean code compared to April 2016. She just needs to learn how to work with people face to face, through mocking interview experience, she has less emotions.

Problem solving rating 

Last 2 experience, in the problem solving category, first time she got rating 2 of 7, second one is 4 of 7. 4 of 7 is related to "working out a brute force solution". Even though the first two mock interviewers are totally different in technical skills, but one thing is common. Optimal solution is the king, need to do some study on space and time tradeoff. 

Time complexity is much more important to battle, using space to trade time complexity. Processing something first and save into memory, using as less as time as possible.

Mocking season 

She missed the first two months of practice from January to March. Usually this is the season a lot of high competitive players are practising mocking experience, Julia should have chance to meet a lot of good players and learn from the experience.

Algorithm

Statistics 

Problem solving skills - 4 out 7

Follow up 

May 29, 2017

1.  using HashSet to find unique numbers.
Leetcode 18 - 4 sum, C# practice is here.
2. Try not to use HashSet, and see if it is solvable.