How did you solve question number 4. I mean brute force is way too hard and without any clever algorithm it is almost impossible??
@rahulchhabra07 Do it the greedy way. Start making trips. Its meant to be done with pen and paper not a computer. Although I donāt see why a computer generated solution of brute force will be hard in this case. Think again and read the question multiple times. Iām sure you got confused. This is an easy question and one can easily score 20 marks in this. Even though I scored 10. 
@Organic-Shilling well i did get 20, but my method was very time consuming. I created a table of every letter coming and the maximum flights to every position till then. this would finally give the maximum fights to get to 2. But is there any better algorithm?
Update:sorry, the answer is not 127, 123 is the highest
Are 90, 146 and 585 for question 2 confirmed? Because those are what I got too.
Well for Q2 , how can train 5 enter BEFORE train 1??
I have a feasible solution as in the image
E1 __ __ __ __ __ __ __ __ __ E6 L6 (since each train can come in a specific orderā¦)
Here E1 means train has Entered while its train no 1
Since we know when can each train go, we can find no. of ways
We first select the position of E2 then E3 ā¦ When we are at last node ,we note no of ways ,move up a branch and similarily find all the ways
I am damn sure this answer is correct
@c1_6 Depends on what you mean by confirmed.
I wrote a program that basically checks every possible sequence and then reports the total number of valid sequences, which agreed with this answer.
There is no official confirmation though.
Edit: Hereās my explanation:
http://discuss.codechef.com/questions/56777/zio-2015-discussion?page=1#56884
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@superty I tried reading your answer, but my notation and method was far different ā¦ basically brute force.
Will an answer key be released? And is it true that the cut-off is 30 for class 11th students?
Youāre right. I saw a flaw in my answerā¦
I assumed that the sequence EEEELLLLEELL is an illegal sequence but as it turns out my answer is incomplete
Point to the current airport with a pencil, read the next flight code and keep moving. The number of places where one has 2 choices are limited. In computer science terms be greedy while making decisions, where your greediness can foresee the next few airports and make change decisions accordingly.
Yep Confirmed. Congrats.
EDIT: By confirmed it means we have a list of all possible sequences and nobody has found a contradiction in them. See the comments of the answer on the top. Go through them, if you find a contradiction in a case or a missed case we are doomed.
@sidmohla 125346 is possible as --> 6 enters and leaves, 5 enters, 4 enters and leaves, 3 enters and leaves, 5 leaves, 2 enters and leaves, 1 enters and leaves. What are you final answers for this question.
Nobody knows the cut offs yet. But 30 for 11th seems reasonable to me.
So How many marks is everybody getting ? Mention your marks and class in the comments.
50 marks 12th grade
No reputation == No comments
Also I am class 12 and marks are 40 (two epic mistakes in one sub part each of Q1 and Q3 + total downfall in Q2).
Very less students appeared for ZIO this year. You have a good chance. Are you giving ZCO ?
I did it using semi brute force and I got those same 3 numbers so if there is a missed case, I missed it too.
If the answers in the original post are all correct, Iām getting 70 so no problem there.