HackerRank codesprint - Array construction - after contest (series 2 of 5)

Nov. 14, 2016

Problem statement:
https://www.hackerrank.com/contests/university-codesprint/challenges/array-construction/submissions/code/7825209

Study C# submissions:
1. perfect solution with full score 80
https://gist.github.com/jianminchen/096ebc5bc1769b83b38ec6eeaabbc7c5

Julia spent more than one hour to read code, but she could not understand the design. So, she decided to work on debugging, add output text info to figure out the design.

Here are workout she did and then figured out the algorithm:

Study more than 2 hours on one of solutions, using recursive solution; but Julia still are not clear about the solution. Need to work on more! Do not give up! Try it every day 10 minutes. It should be easy! 

Julia's work (3+ hours) Try very hard to understand the clever solution by debugging 

-  From the above C# solution:

https://gist.github.com/jianminchen/096ebc5bc1769b83b38ec6eeaabbc7c5

-->   add some debug information to understand the algorithm 

add debugging information to the source code 

https://gist.github.com/jianminchen/48616cdb58a96264eb6e17ce8b177005

-> Here is the log file to understand the algorithm design:

https://gist.github.com/jianminchen/a05ab342cf882989c94197e7ca2dc9bd

Question 1:

Use your own words to guess how to design the algorithm through debugging process?

Answer:

still confused about line 118, line 119:

118  int newSum     = sum + i * (n - p);

119  int newDiffSum = diffsum + (i * p - sum) * (n - p);

Question 2: What does (n-p) stand for? Can you explain it in one sentence?

Let us work on one more change first:

https://gist.github.com/jianminchen/48616cdb58a96264eb6e17ce8b177005

so, decided to track n-p value on line 118.

C# code with debug info (stage II):

https://gist.github.com/jianminchen/f258bab2e8047ada3da94202f1cb8adb

debug text info:

https://gist.github.com/jianminchen/d438d60381f2193d0dfba3a7fa10137c

Actionable Items:

1. Run test cases, and compare the time difference 

First, comment out code on line 36, time out on test case 4.

https://gist.github.com/jianminchen/096ebc5bc1769b83b38ec6eeaabbc7c5

Write a new blog on this testing adventure.

http://juliachencoding.blogspot.ca/2016/11/hackerrank-university-codesprint-array_18.html

2. Study all C# solutions:

2.1. perfect solution with full score 80

https://gist.github.com/jianminchen/49f45acc69b4d87c51d02c81a788fbc9

2.2. perfect solution with full score 80

https://gist.github.com/jianminchen/096ebc5bc1769b83b38ec6eeaabbc7c5

2.3. score half score 40

https://gist.github.com/jianminchen/f85de0c2b6014ff79d1097ce12705691

3. understand one term: constructive algorithm

Constructive algorithm: (preprocessing, and then, lookup)

(HackerRank - array construction is a constructive algo.)

https://www.quora.com/What-does-the-constructive-algorithms-tag-mean-at-Codeforces 

Great idea to push hard - cannot get it wrong! that is the attitude for advanced level algorithm involved mathematical analyse.

Don't practice 'til you get it right. Practice 'til you can't get it wrong. #tennis #motivation pic.twitter.com/GNpWdF372B

— Tennis Coaching™️ (@tennisdothow) August 20, 2015