Vovuh's blog

By Vovuh, history, 3 weeks ago, In English,

1144A - Diverse Strings

Idea: MikeMirzayanov

Tutorial
Solution

1144B - Parity Alternated Deletions

Idea: MikeMirzayanov

Tutorial
Solution

1144C - Two Shuffled Sequences

Idea: MikeMirzayanov

Tutorial
Solution

1144D - Equalize Them All

Idea: Vovuh

Tutorial
Solution

1144E - Median String

Idea: Vovuh

Tutorial
Solution

1144F - Graph Without Long Directed Paths

Idea: MikeMirzayanov

Tutorial
Solution

1144G - Two Merged Sequences

There is different solution for the problem, it is pretty interesting! Thanks, Roundgod!

Idea: Vovuh

Tutorial
Solution
 
 
 
 
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3 weeks ago, # |
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thank you

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3 weeks ago, # |
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G Tutorial is not available?

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3 weeks ago, # |
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Thanks For Fast Editorials <3

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3 weeks ago, # |
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In Problem G, I'm getting WA on test 12. Please help me out. 52149636

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3 weeks ago, # |
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Why is problem D tagged as dfs and similar?

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3 weeks ago, # |
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Interesting idea on E, very cool problem!

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3 weeks ago, # |
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Solving E problem using Python gave TLE, don't know why. I stored the Number as int(base 26). Shouldn't it work?

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    3 weeks ago, # ^ |
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    Nobody can see your submitted solutions. You're probably getting TLE because the operations you are doing on the numbers are too slow.

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      3 weeks ago, # ^ |
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      No problem, I think I got the Reason why it is giving TLE.

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3 weeks ago, # |
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I don't understand E's editorial,can anyone please explain?What are we doing? I thought of seeing the string as base 26,so we can convert it into decimal and take the mean. For example: az = 26^0*25 + 26^1*0 = 25, bf = 26^0*5 + 26^1*1 = 31 now taking the mean we get 28,converting into base 26 we get 12 (26^0*2+26^1*1 = 28),which is bc. But for large string lengths we may have to do 26^100000,so I thought it is not feasible. What are we doing in this editorial?

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    3 weeks ago, # ^ |
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    You misunderstood the meaning.We can represent the string to a number, with base 26. And then we can figure out that if string s is lexicographically smaller than t, the "number" which s represents is smaller than t's "number". So what we need to calculate is a "number" which is the median of [s's number, t's number]. We can Easily calculate it by writing "BigIntegar", to storing big number and doing operations. Here's my Code Link: Here

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      3 weeks ago, # ^ |
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      Thanks a lot for replying,in author's code,I understand the string is stored as int with base 26,but what are the 2 operations done? Is he adding the 2 vectors?

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        3 weeks ago, # ^ |
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        2 vectors represents 2 BigInt(base 26). so, now he add the BigInt and then divide it by 2. (Same as we did addition and division with paper and pencil in childhood :) )

        Then print the vector as characters.

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3 weeks ago, # |
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This is a real Div.3 :)

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3 weeks ago, # |
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Another solution to G by considering whether the max.element in the array is in the decreasing or increasing subsequence:52159992

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3 weeks ago, # |
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anyone please help. In problem F, why my code give me Runtime Error on test 15?.

My Submission: 52160039

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3 weeks ago, # |
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Runtime error in F: can someone help me debug: https://codeforces.com/contest/1144/submission/52208937

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    3 weeks ago, # ^ |
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    maybe it's the for-loop for finding the largest degree

    you iterate it for i = [0, m), while vector "graph" has the size of n. RTE when m > n.

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3 weeks ago, # |
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for E:someone plzz explain how division by 2 is done in 26 base

for (int i = 0; i <= k; ++i)

{

    int rem = a[i] % 2;

    a[i] /= 2;

    if (i + 1 <= k) {

       a[i + 1] += rem * 26;

    } else {

       assert(rem == 0);

}

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    3 weeks ago, # ^ |
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    If the digit in the pos[i] is not divisible by 2, you can just pass a one to the next digit, a 1 from $$$1*26^i$$$ is equivalent to 26 in $$$26^\left( i-1 \right)$$$, if it is divisible by 2 then you just need to divide it by 2

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problem ID:1144F

problem F is also done by BFS

problem F code(happy coding)

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3 weeks ago, # |
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Can I solve E using big integer?

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    3 weeks ago, # ^ |
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    You will end up with TLE if you try to actually find the values in base 26. Instead try to understand how you can divide the representation in base 26 by 2. In such a case you will not need BigInteger.

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3 weeks ago, # |
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for problem g is this correct approach? let say i have two array X(increasing),Y(decreasing) and A is Merge(X,Y). Find the longest increasing sequence of A this sequence will contain X and atmost one element of Y and after removing that element from Y Y will still remain decreasing.

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3 weeks ago, # |
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Why is this solution for E giving TLE? https://codeforces.com/contest/1144/submission/52223063

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    3 weeks ago, # ^ |
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    You are doing ans = ans + (char)(median[i] + 'a'); This takes more time as compared to ans+=(char)(median[i] + 'a'); I am not sure of its reason. But i too have faced similar issues before.

    Can someone explain why this removes TLE?

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3 weeks ago, # |
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Problem E is very badly explained.

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3 weeks ago, # |
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there is a another way to solve problem G
first we found the LIS of the array and then there is a fact : if we can split the given sequence a into one increasing sequence and one decreasing sequence then at most one of the elements of the LIS could not appear in x ( x is the increasing sequence ) otherwise in the y ( the decreasing sequence ) we have two numbers A , B which a[A] < a[B] and A < B and its impossible so if we fix which index i is not gonna appear in x we can solve the problem

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In problem E, why is it only allowed to do a[i] %= 26 when i > 0?

For this test case, for example:

6

nijfvj

tvqhwp

The sum in the base 26 is: 33 3 25 13 17 24

Why is it allowed to have this "33" in the first position?

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    3 weeks ago, # ^ |
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    In my program,its allow a[i] % 26 in i = 0

    but if u do that, you need to deal with leading zeros,it's a little bit more trouble, but it doesn't really matter.

    For example

    33 3 25 13 17 24 -> 1 7 3 25 13 17 24

    then u div 2

    0 16 14 25 19 21 25

    now,u need cheak the zero,if u dont do that ,the answer will be an extra a

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Thanks for these tutorials. But I do not know how to solve the problem G with Greedy. So maybe I need help. QAQ.

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Help me! I dont understand print problem F in tutorial: cout << (color[e[i].first] < color[e[i].second]); ???????????? please

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    3 weeks ago, # ^ |
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    when you split vertices in to two part . you want obtain direct of edges such that every edge in part one direct to the second pare or you can direct all edges from second part to the first part . and we know that every edges has two end point such that one of them from first and one of them from second (because its bipartite) so if color[first endpoint] < color[second endpoint] that means color[first endpoint] = 0 so that condition return 1 and otherwise return 0

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In editorial 'G',what is the meaning of 'maximum possible minimal'?

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    3 weeks ago, # ^ |
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    minimal element from the sequence is a const value , this const value be maximum as possible means .

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Somebody please tell me why this submission 52323233 works but this submission 52321524 does not ??

The only difference in both the codes is that in accepted one, I've accepted the input as strings while in wrong answer I've accepted them in character arrays

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Who can help me for my submission on F: My submission for F I can pass when n=2e5 and m=2e5,but it will TLE on test 12(it's n=1e5 and m=2e5) and when it TLE,it run 10000~20000 edges. I think my code is an solution O(mlog(m)) Thank you!

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9 days ago, # |
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For Problem E

First each letter in string is converted to corresponding number, ie a = 0 , b = 1 , c= 2....(This is base 26 representation) and is stored in two vectors a and b.

After that to add these vectors we can't do it normaly because it is in base-26 and not in base-10(decimal).

So refer this video for addition of numbers which are not of base-10(decimal) -> https://www.youtube.com/watch?v=O-CwMsS0eNw

So when addition of two digits becomes more than 26 we add 1(carry) to next digit and mod 26 with current digit(equivalent to number — 26).

The division part is explained by Sam in another comment.