yash_daga's blog

Invitation to CodeChef Starters 142(Rated till 5-Stars) — 10th July
By yash_daga, history, 4 months ago, In English

We invite you to participate in CodeChef’s Starters142, this Wednesday, 10th July, rated for till 5-Stars(ie. for users with rating < 2200).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

Note: Some problems have subtasks

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

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4 months ago, # |
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Hoping no problems will be there containing Game Theory. IMHO, CC should give Game Theory some rest.

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4 months ago, # |
  Vote: I like it +24 Vote: I do not like it

BERNARD orz

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4 months ago, # |
  Vote: I like it +14 Vote: I do not like it

Another week another contest not rated for 7* coders :sob;

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4 months ago, # |
  Vote: I like it +3 Vote: I do not like it

Amr Harb is the best.

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4 months ago, # |
  Vote: I like it +8 Vote: I do not like it

Whenever you have subtasks you must have separate samples where sample 1 fits the constraints of subtask 1, sample 2 fits the constraints of subtask 2, etc.

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    4 months ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    And explanations of samples must be after all tests.

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4 months ago, # |
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SpeedChef

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4 months ago, # |
  Vote: I like it +4 Vote: I do not like it

Was anyone able to solve Sum of Xors(SMXR)?

I thought it would be just (N*M*3)/2 but that's wrong, can someone please explain?

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    4 months ago, # ^ |
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    Try to think when K=6 and N=M=4.

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      4 months ago, # ^ |
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      That was such a random guess, it is not a coding problem.

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        4 months ago, # ^ |
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        What will happen when K is of 4*x+2 form? Do you think this is random guessing?

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          4 months ago, # ^ |
          ← Rev. 2   Vote: I like it +3 Vote: I do not like it

          I looked at $$$N=M=4$$$, $$$K=6$$$ and immediately guessed that $$$F(K)=0$$$ for all $$$K$$$ except $$$2$$$ and $$$NM-2$$$, without proving that such a 'closed tour' actually exists.

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            4 months ago, # ^ |
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            As a matter of fact, one does not need a closed tour of alternating row and column moves for the construction, which further shows that my guess was not supported by much thought. For example, $$$N=M=6$$$, $$$K=10$$$ has a construction that is not a connected tour:

            ##....
.##...
#.#...
...##.
...##.
......
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            4 months ago, # ^ |
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            That may be your experience.

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              4 months ago, # ^ |
              ← Rev. 2   Vote: I like it +13 Vote: I do not like it

              You know most people are guessing and not even trying to prove when accuracy is 8.2% (Div. 1), 1.23% (Div. 2), 0.6% (Div. 3), and 0.84% (Div. 4).

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      4 months ago, # ^ |
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      The comment below shows the correct arrangement not the one I cooked up.

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      4 months ago, # ^ |
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      Why is the sample test cases promoting the answer (n*m*3)/2? It would have been better if you had included similar corner cases in the samples.

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        4 months ago, # ^ |
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        Sample test cases are made to explain the problem statement, not to include corner cases.

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    4 months ago, # ^ |
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    You can get $$$F(X) = 0$$$ for $$$K \equiv 2 (\mod 4)$$$ for some constructions.

    For example, consider $$$N = 4, M = 4, K = 6$$$

    ##..
.##.
#.#.
....
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4 months ago, # |
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[WRONG]

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    4 months ago, # ^ |
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    Sorting the array completely breaks the number of $$$[L, R]$$$ that satisfy the equation.

    For example consider the input:

    $$$n = 6, x = 1, A = [8, 8, 4, 4, 8, 8]$$$

    In this array, only $$$i = 3, j = 4$$$ satisfy the equation, so $$$F(L, R) = 1$$$ for all $$$1 \leq L \leq 3, 4 \leq R \leq 6$$$ giving an answer of $$$9$$$.

    However, if you sort the array, it becomes $$$[4, 4, 8, 8, 8, 8]$$$ which has $$$F(L, R) = 1$$$ for $$$L = 1, 2 \leq R \leq 6$$$ giving an answer of only $$$5$$$.

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4 months ago, # |
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Not a fan of "knowledge-based" problems like "Number Hunt". Its pretty much just "Do you know that the prime gap is small even at $$$10^9$$$?".

Maybe it makes sense to put it in Starters since they are meant to be "educational" contests, but it still feels out of place.

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4 months ago, # |
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I think anyone who solved this problem before can solve today's sum of Xor in 2-3 minutes

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4 months ago, # |
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Today's E (LENGTHX) , its editorial was based on segment trees , any suggestions where to learn seg trees from ?

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4 months ago, # |
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For xor sum , to prove all even $$$i \gt 4$$$ and $$$i \lt NM - 2$$$ , $$$F[i] = 0 $$$ , you can first construct $$$K = 6.$$$ However , it may get confusing when many $$$1s$$$ have been filled , to solve that case , observe that You can invert all $$$1s$$$ to $$$0$$$ and $$$0s$$$ to $$$1$$$ , and $$$F[i]$$$ remains same. Hence the case $$$K = 6$$$ is same as $$$K = NM - 6$$$ .

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4 months ago, # |
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include <bits/stdc++.h>

using namespace std;

int main() { int t; cin >> t; while (t--) { int n; cin >> n; vector v(n); int y = 0; for (int i = 0; i < n; ++i) { cin >> v[i]; y = y | v[i]; }

for (int i = 31; i >= 0; i--) {
        if ((y & (1 << i)) == 0) {
            for (int j = 0; j < n; j++) {
                if (((v[j])> (pow(2,i)))) {
                    v[j] = -1;
                }
            }
        }
    }
    int a = count(v.begin(), v.end(), -1);
    cout << a << "\n";
}
return 0;

}this code is for 4th que of div4 in codechef(array removal) and it got accepted in codechef but this code gives wrong output for the input(n=4) {2,8,9,10}

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4 months ago, # |
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are u gonna do anything about wrong submissions that got accepted for array removal problem,it had massive impact in rankings of div2

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4 months ago, # |
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Cheaters Cheaters everywhere :

https://www.youtube.com/watch?v=lroJG3QAcRA

Today I was hoping to turn three star on Codechef but thanks to them

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4 months ago, # |
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Sorry for mentioning you but the tester's code given for the problem Pairs Sum with Length x in today's contest does not work. Please fix it.
Submission link
mexomerf IceKnight1093.

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    4 months ago, # ^ |
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    There must be a mistake, this solution is for a prev version of the problem

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4 months ago, # |
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Number Hunt Detailed Video Editorial

https://youtu.be/fhOLz-Or9NA

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