Introduction
What is Code Hunt?
On May 15th, as seen
on Reddit the Microsoft Research Team
announced Code Hunt, an online "game" that claims to help you learn to code. Not too sure about that, but it is certainly an interesting way to pass the time and may even teach you a few things along the way. Inevitably, though you get stuck and need hints.
This post
The purpose of this post is not to give you all the answers to Code Hunt. If you're looking for that, you're in the wrong place! What it will do is explain how to find all the answers and why your answers are not optimal. With the information given here, you should be able to receive full marks and learn something along the way. We only use C# here, but the information can equally be applied to Java.
Resources
You may find use for:
Walkthrough
Sign up
First things first, sign up and log in to ensure that you keep your progress between sessions.
General approach
The problems do not come with any specification of what the tested method should achieve, so the first thing is to reverse engineer the specification from the input->output expectations presented by the system. One approach to achieving this is to use concatenated ternary operators using the tested input parameters as follows:
Once you have reverse engineered the method's intended purpose, you should apply documentation comments with triple-slashes. Always document your code!
Finally, implement the function as efficiently as you can:
If Microsoft agree that your code is both correct and succinct, you get maximum points!
00 Training
00.02 Inky fingers
Look at the input value. Look at the output value. Not much difference is there?
00.03 Doubly tricky
Output is a multiple of input.
00.04 Nonplussed?
Output combines inputs.
01 Arithmetic
01.01 Are you positive?
Output is a simple function of input.
01.02 A bit more different
Add a constant to the input value.
01.03 Don't be so square
A higher order function.
01.04 Magic numbers
A lower order function
01.05 Divide and conquer
Magic!
01.06 More over?
Sounds like...
01.07 What's the difference?
Why fewer?
01.08 Why try more?
...than x. First order.
01.09 You star!
Go forth...
01.10 Tricky
The first one, the second third.
01.11 Get this one over with
The other goes down under.
01.12 A modern approach
Read up on the modulo operator (the percent sign).
01.13 Even more modern
Similar to the previous puzzle. But more. so.
01.14 WHAT?!
I must confess, originally I only managed to get the following:
It then took a LOT of staring to realise that this was some sort of modulo, but I didn't get it. Thanks and kudos go to MegjelenőNév for pointing out that this one requires x both before AND after the modulo. Spoiler: answer in comments below.
01.14 Of Average difficulty
You know what I mean.
02 Loops
Now the loops can all be achieved using regular loops, but in this modern age of LINQ, who uses loops? I have provided all my Linq-based answers. Please work out WHY these are correct (though not necessarily the highest-scoring) answers...
02.01 Simple Range
Read up on The LINQ Range method. It may not do what you think!
02.02 Squares
02.03 More Squares
02.04 Add 'em up
This one is a little weird and requires a pair of casts...
02.05 One fewer squares
02.06 Count the a's
02.07 Count the input chars
03 Loops 2
03.01 Ternary operator
For this one, I AM going to directly give you the right answer, and it's a single line. Read up on the C# ternary operator to find out how this works...
return power==0?1:power==1?number:number*Puzzle(number, power-1);
Here's how to read the above...
Return the following value:
- If power is 0 then 1 otherwise
- If the power is 1 then number otherwise
- The number multiplied by a recursive call to this function against the number but for one lower power.
03.02 LINQ Aggregate
For this one, again, I am going to give you the answer. Read up on the LINQ Aggregate function, which recursively multiplies. You should then be able to see why this is an acceptable solution:
return Enumerable.Range(1,i).Aggregate(1, (x,y) => x * y);
03.03 More Range, More Aggregate
Now that you have the answer to 03.02, you should be able to solve 03.03. Of course, you read up on exactly how LINQ Range works didn't you? No? Shame! Go read up on EXACTLY what each term does.
Now, can you explain why this works?:
return Enumerable.Range(lowerBound,upperBound-lowerBound).Aggregate(upperBound, (soFar,newValue) => soFar * newValue);
03.04 Wot no LINQ?
No LINQ needed for this one really... Half one fewer by half one more.
03.05 Non-optimal LINQ
Enumerable.Range(1, upperBound).Sum(a=>a%2==upperBound%2?a*a:0);
Now make it optimal.
03.06 LINQ Repeat
Here's part of the answer. Now if only there were a way of JOINing STRINGs...
Enumerable.Repeat('_', word.Length)
03.07 Casting to int
Here's a framework.
return new string(s.ToCharArray().Select(c=>(char)(MATHS!).ToArray());
Hint: you can cast a char as an int.
03.08 I am not a number!
I'm a free string!
04 Conditionals
04.01 OR
04.02 AND
04.03 LESS THAN
04.04 LESS THAN again
04.05 i<0?-1MYSTERYCHARACTERi>0?1:0
04.06 MORE THAN
04.07 i<WHAT?NUM:ANOTHERNUM
04.08 Modulo ternary string / string
04.09 (i%NUM!=0?STRING1:STRING2) + STRING3
One is empty - which one?
04.10 Similar to the previous
04.11 Redouble?
04.12 i<NUM1?NUM2:i<NUM3?NUM4:NUM5
05 Conditionals 2
05.01 Oh, simple ternary
05.02 LINQ distinct count
05.03 What sort of triangle?
05.04 Show us those abdominals!
05.05 Square equality
06 Strings
06.01 I did not write elegant code.
But then I didn't need to!?
06.02 Non-optimal - make it better
var charArray = s.ToCharArray();
return Enumerable.Range(0,charArray.Length).Select(n=>n%2==0?charArray[n].ToString().ToUpper():charArray[n].ToString()).Aggregate((a,b)=>a+b);
06.03 Reverse, split, uppercasefirst, join, reverse
06.04 s at x
06.05 one plus two
06.06 second half
06.07 upper lesser second half + second half
06.08 which is longer?
06.09 the longer or both
06.10 third
06.11 WHAT?! again
See Andrew Furdell's hint below.
06.12 string + reverse
07 Strings 2
07.01 two three one one three two
07.02 first half
07.03 replace b with c
07.04 reverse
07.05 stringbuilder every other use mod
07.06 use string.Replace()
07.07 Vwls r bd m'ky?
07.08 Everything seems to be in order
Use IndexOf
07.09 Enumerable Repeat string Join
Do it all in one line
07.10 Hmm
I have the following:
var alphabet = "a b c d e f g h i j k l m n o p q r s t u v w x y z";
return string.Join(" ",Enumerable.Range(0,t).Select(n=>n!=t-1?alphabet:alphabet.Substring(0,50-n*2) + "z").ToArray());
Now how to improve?
08 Nested Loops
OK, so everyone can write nested for loops. But we're better than that now aren't we? ;-) Unfortunately, these efforts are not appreciated by Microsoft so most of these are considered non-optimal answers. IF that is the case, there is something wrong either with their compiler optimisations, or with their code evaluation algorithm.
08.01 Factorial sums
Now Microsoft have just got this one plain wrong. The following code is a quite reasonable attempt to sum the factorials between i and j:
return Enumerable.Range(i, j-i+1).Sum(x=>Enumerable.Range(1,x).Aggregate((a, b) => b * a));
However, this get rejected for two really weird cases:
For input values of i=12, j=13, Microsoft give the answer -1883912192. Clearly wrong. 12! + 13! is 6706022400.
For input values of i=3, j=64, Microsoft gives the answer null. Null?! Null is not even a legitimate return value. Don't bother with this one, it can't be done.
UPDATE: Kudos to MW, who (SPOILER) has given a full 3-star answer in the comments, below.
08.02 Hashes
This one is easy to do with nested loops or new string('#', x), but can you do it with LINQ?
Here's the kind of code you should be writing by now...:
return string.Join("", Enumerable.Range(1,n).Select(a=>new string('#', a) + " "))
08.03 Alpha underscores
Easy to see what they are wanting here, and easy to lazily implement in for loops.
Microsoft didn't give full marks to the following, so I don't feel bad about sharing the following:
return string.Join("", Enumerable.Range(0,n+1).Select(a=>string.Join("",Enumerable.Range(0,n+1).Select(x=>x>a?"_":x.ToString())) + " "));
08.04 Dash on N
More LINQ awesomeness:
return string.Join(" ",Enumerable.Range(1,n).Select(a=>string.Join("", Enumerable.Range(1,n).Select(y=>y!=a?b:"-"))));
08.05 Underscore at N
Blah blah LINQ blah:
return string.Join(" ",Enumerable.Range(0,a.Length).Select(b=>string.Join("", Enumerable.Range(0,a.Length).Select(y=>y!=b?a.Substring(y,1):"_"))));
08.06 Have LINQ hammer. Everything is a nail.
return string.Join(" ",Enumerable.Range(1,size).Select(b=>string.Join("", Enumerable.Range(1,size).Select(y=>b!=1&&b!=size&&y!=1&&y!=size?"_":"$"))));
08.07 LINQ -> Noughts and Crosses
return string.Join(" ",Enumerable.Range(0,height).Select(heightPos=>string.Join("", Enumerable.Range(0,width).Select(widthPos=>(widthPos+heightPos)%2==0?"x":"o"))));
08.08 OK, I admit, not pretty, but I'm committed to it now...
I will tidy this one up later with Math.Abs()...
return
string.Join(" ",Enumerable.Range(1,number).Select(index=>string.Join("", Enumerable.Range(0,index).Select(a=>index.ToString()))))
+ " " +
string.Join(" ",Enumerable.Range(1,number-1).Select(index=>string.Join("", Enumerable.Range(0,number - index).Select(a=>(number-index).ToString()))));
09 1D Arrays
09.01 list at i
09.02 First and last
09.03 LINQ Contains()
09.04 Enumerable.Range
09.05 Enumerable.Range again
09.06 And again...
09.06 And again...
09.07 ToCharArray then LINQ then back to String
09.08 Enumerable.Range again
09.09 Select a=> -a
09.10 Array.Reverse()
09.11 To CharArray, Reverse and Join
09.12 Buggy test?
My answer here is
return Enumerable.Range(numbers.Length-amount, numbers.Length).Select(a=>numbers[a%numbers.Length]).ToArray();
This results in...
I have NO idea.
UPDATE: Kudos to MW, who (SPOILER) has given a full 3-star answer in the comments, below.
09.13 Coming soon...
09.14 Enumerable.Range with Math.Max and Select
10 Jagged Arrays
All the following can be used to get 3 stars
10.01 List at i,j
10.02 Three star answer...
You need to use Enumerable.Repeat<T>.
10.03 Same as previous
10.04 Nested projections
10.05 Same as before, but use Sum() with a ternary
10.06 Same as before, but use Max()
10.07 Coming soon...
10.08 Larger of the sum of the last or sum of the first
11 Arrays 2
11.01 Zip, Concat and Skip
11.02 SelectMany() flattens
11.03 This one makes me cross..
Can someone explain to me why this does not work?!
return
Enumerable.Range(0, input.Length).Sum(arrayIndex=>(long)input[arrayIndex][arrayIndex])
==
Enumerable.Range(0, input.Length).Sum(arrayIndex=>(long)input[arrayIndex][input.Length-1-arrayIndex])
;
11.04 The modern way is Linq
11.05 string + condition?string:string.Empty
11.06 Linq t?"E":r?"N":a?"R":"Y"
11.07 Linq to Pivot using Enumerable.Range and [y][x]
12 Search Sort
12.01 .Count ==
12.02 Same again
12.03 Cleverness gives 1*
Use FirstOrDefault()
list.Select((item, index) => new { Item = item, Index = index })
12.04 Same but LastOrDefault() instead
12.05 Same but ToArray()
12.06 Simple Select()
12.07 Pairs sum
12.08 Coming soon...
12.09 Ever increasing
12.10 Distinct Count
12.11 Array.Sort()
12.12 Yes, it works for strings too!
13 Cyphers
13.01 int cast +7 %26 -97
13.02 Different mod, different base
13.03 Different offset per character
13.04 nn mm nineteen nineteen
14 Puzzles
14.01 Sum
14.02 6003
14.03 Coming soon...
14.04 Coming soon...
