butterflies's blog

By butterflies, history, 6 weeks ago, In English

Hi Codeforces,

I created Starlight Problem Solving to help people view insights and find similar problems for various coding contest problems (e.g. Codeforces, AtCoder). This allows people to get an idea of problem solving strategies that are important to MASTER in addition to standard algorithms and to continue practicing problem solving strategies they struggle with to improve mastery.

Right now, we need more data for this to be helpful. Also with more data, we can predict insights and summarize the key insights needed to achieve a certain level.

I've tried getting users to submit insights through giftcard giveaways and also by importing Google Forms for their spreadsheets of insights of problems: https://starlightps.org/import/. However, this hasn't been too effective.

Any suggestions on how to get people to submit insights for various coding contests problems to create a helpful resource?

Thanks a lot!

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By butterflies, history, 4 months ago, In English

Hi Codeforces!

We would really appreciate it if you could submit spreadsheets containing key insights for problems. This will help us build Starlight Problem Solving (https://starlightps.org), where users can see key insights for various competitive coding problems to keep in mind for future problems, and find similar problems given insights they struggled with. This website aims to help people master key insights needed in addition to algorithms to improve their skills.

🔢 Steps Needed

  1. Please create an account on https://starlightps.org
  2. Please fill out this Google Form: https://forms.gle/PbgUqM7qapwKk3Jv7
  3. Monitor your status at https://starlightps.org/import/
Submit Spreadsheets through Google Form
Monitor the status of your import

Now, more detailed information on Starlight Problem Solving

  • 🙋 You can share and view a summary of insights (thanks to AI) on over 20,000 problems (Codeforces, AtCoder, DMOJ, etc). This allows you to see new important insights you may be missing on finding.
  • 🔍 You can also view similar problems based on insights (thanks to AI) so if you couldn't solve a problem, you can now find similar problems to allow you to master the insight(s) you struggled with.
  • 🤔 You can also see hints to spend more time with hands on problem solving.
  • 🏗 In the future, we hope to create an AI to predict key insights problems (including ones with no insights in this database) and use AI to summarize the key insights needed to achieve a certain level (e.g. USA computing olympiad gold, codeforces rating 1900) since problem solving skills in addition to algorithms is needed.

If this sounds like it would be useful, please consider joining the website. Let as many people know as possible (links of text to copy in share the message) as we likely NEED data on MANY TYPES of problems. Use the JOURNAL FEATURE which stores all the insights of problems you solved!

Join the website → starlightps.org

💬 Join the community:

Join the Discord server: https://discord.gg/czgReQSpFz to share your input on how to improve this project/features to add!

🌐 Share this message:

Markdown format of various ads, as well as a short text add, and an image promoting starlight are all available at https://tinyurl.com/starlightps-ads. All available under CC BY 4.0.

👐 Join the project (volunteer, open source)!

We are currently open source on GitHub: https://github.com/bkf2020/starlight. Licensed under AGPLv3.

Here is a Google Form to fill out with your qualifications if you are interested: https://forms.gle/txpWvcZwWxD1yVog6. I'm looking for machine learning engineers, web developers, web designers, and marketing/outreach.

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By butterflies, history, 4 months ago, In English
starlightps.org

Hi Codeforces!

We would really appreciate it if you could submit spreadsheets containing key insights for problems. This will help us build Starlight Problem Solving (https://starlightps.org), where users can see key insights for various competitive coding problems to keep in mind for future problems, and find similar problems given insights they struggled with. This website aims to help people master key insights needed in addition to algorithms to improve their skills.

🪜 Steps Needed

  1. Please create an account on https://starlightps.org
  2. Please fill out this Google Form: https://forms.gle/PbgUqM7qapwKk3Jv7
  3. Monitor your status at https://starlightps.org/import/
Submit Spreadsheets through Google Form Monitor the status of your import

Now, more detailed information on Starlight Problem Solving

  • 🙋 You can share and view a summary of insights (thanks to AI) on over 20,000 problems (Codeforces, AtCoder, DMOJ, etc). This allows you to see new important insights you may be missing on finding.
  • 🔍 You can also view similar problems based on insights (thanks to AI) so if you couldn't solve a problem, you can now find similar problems to allow you to master the insight(s) you struggled with.
  • 🤔 You can also see hints to spend more time with hands on problem solving.
  • 🏗 In the future, we hope to create an AI to predict key insights problems (including ones with no insights in this database) and use AI to summarize the key insights needed to achieve a certain level (e.g. USA computing olympiad gold, codeforces rating 1900) since problem solving skills in addition to algorithms is needed.

If this sounds like it would be useful, please consider joining the website. Let as many people know as possible (links of text to copy in share the message) as we likely NEED data on MANY TYPES of problems. Use the JOURNAL FEATURE which stores all the insights of problems you solved!

Join the website → starlightps.org

💬 Join the community:

Join the Discord server: https://discord.gg/czgReQSpFz to share your input on how to improve this project/features to add!

🌐 Share this message:

Markdown format of various ads, as well as a short text add, and an image promoting starlight are all available at https://tinyurl.com/starlightps-ads. All available under CC BY 4.0.

👐 Join the project (volunteer, open source)!

We are currently open source on GitHub: https://github.com/bkf2020/starlight. Licensed under AGPLv3.

Here is a Google Form to fill out with your qualifications if you are interested: https://forms.gle/txpWvcZwWxD1yVog6. I'm looking for machine learning engineers, web developers, web designers, and marketing/outreach.

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By butterflies, history, 6 months ago, In English

Hi Codeforces!

We're doing a 30 day problem solving challenge which ends on October 6, 2023; 04:00 AM UTC. At the end there will be a raffle where one winner gets a gift card up to $100. The value of the gift card will depend on participation, so please share to as many people as possible.

To qualify for the raffle, you must solve at least 15 different problems and submit at least one insight OR hint per problem to the problems in Starlight Problem Solving. You can use old problems you did before, but it will be preferred that you solve new challenging problems. We have some leeway for days you can't solve a problem or need multiple days to think of one problem.

Here are problems to recent Codeforces round to help get you started: Edu Round 154 and Pinely Round 2. Please use the journal feature (https://starlightps.org/journal) to store insights of all problems you solve. Here are details of this on our website: https://starlightps.org/about/challenge/.

Join the website → starlightps.org

Now, posting insights/hints will help us build an AI platform to help problem solvers discover hints/insights on various competitive programming/math problems (Codeforces, AtCoder, DMOJ, etc) so they can learn from others AND find similar problems based on insights they struggled with making their practice more effective. In the future, we hope to create an AI to help predict key insights for problems and summarize the key insights needed to achieve a certain level in contests. More details here: https://codeforces.com/blog/entry/119695.

Here are some other ways to get involved/join the community:

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By butterflies, history, 6 months ago, In English
starlightps.org

Hi Codeforces!

Are you struggling with practicing effectively? Maybe you are having issues with using key insights from previous problems you solved in new problems? (Note: multiple top problem solvers like Geothermal (CF international grandmaster, top 0.02%) recommend reflecting on key ideas/observations 💡 after solving problems in order to be able to tackle new problems.)

Thus, I have created this platform called 🌠 Starlight Problem Solving to help people improve:

  • 🙋 You can share and view a summary of insights (thanks to AI) on over 20,000 problems (Codeforces, AtCoder, DMOJ, etc). This allows you to see new important insights you may be missing on finding.
  • 🔍 You can also view similar problems based on insights (thanks to AI) so if you couldn't solve a problem, you can now find similar problems to allow you to master the insight(s) you struggled with.
  • 🤔 You can also see hints to spend more time with hands on problem solving.
  • 🏗 In the future, we hope to create an AI to predict key insights problems (including ones with no insights in this database) and use AI to summarize the key insights needed to achieve a certain level (e.g. USA computing olympiad gold, codeforces rating 1900) since problem solving skills in addition to algorithms is needed.

If this sounds like it would be useful, please consider joining the website. Let as many people know as possible (links of text to copy in share the message) as we likely NEED data on MANY TYPES of problems. Use the JOURNAL FEATURE which stores all the insights of problems you solved! We are working to add the feature to help import your spreadsheets of insights for your practice to the journal to make it more convenient!

Join the website → starlightps.org

30 day problem solving challenge (win up to $100)

We're doing a 30 day problem solving challenge where one lucky winner will get an Amazon gift card worth up to $100. The prize depends on participation, so please share this challenge. To qualify, you must solve at least 15 problems and post at least one insight/hint for each. More information here: https://starlightps.org/about/challenge/.

We are working to add the feature to help import your spreadsheets of insights for your practice, so we may extend the deadline.

💬 Join the community:

Join the Discord server: https://discord.gg/czgReQSpFz to share your input on how to improve this project/features to add!

🌐 Share this message:

Markdown format of various ads, as well as a short text add, and an image promoting starlight are all available at https://tinyurl.com/starlightps-ads. All available under CC BY 4.0.

👐 Join the project (volunteer, open source)!

We are currently open source on GitHub: https://github.com/bkf2020. Licensed under AGPLv3.

Here is a Google Form to fill out with your qualifications if you are interested: https://forms.gle/txpWvcZwWxD1yVog6. I'm looking for machine learning engineers, web developers, web designers, and marketing/outreach.

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By butterflies, history, 7 months ago, In English

Join the website → starlightps.org

Hi Codeforces!

The top 1% are able to effectively use insights from old problems to solve new problems. Multiple exceptional problem solvers such as SuperJ6 (codeforces [cf] master, top 1%), Geothermal (CF international grandmaster, top 0.02%), and Colin Galen (CF grandmaster, top 0.18%) all recommend reflecting on key ideas/observations 💡 after solving problems in order to be able to tackle new problems in competitive programming.

Therefore, I created this AI platform called 🌠 Starlight Problem Solving to allow problem solvers to:

  • 🙋 Share these key insights/observations as well as hints for over 20,000 problems including Codeforces, USA Computing Olympiad, American Math Competitions (AMC) 8/10/12/AIME/USA(J)MO, AtCoder and DMOJ
  • 🧠 Summarize key insights/hints with artificial intelligence (AI/ML) and see the key insights that other top problem solvers are thinking of a problem.
  • 🔍 Find similar problems based on insight(s) of one problem to continue practicing insights/observations you struggled with applying/seeing in a problem.
  • 🤔 See hints to be able to take more away from more time spent on hands on problem solving.
  • 📕 A Journal to store the statuses of all problems you are solving and the key insights used making it convenient to use this website. ( Help out other problem solvers by using this feature to store the key insights for each problem you solve! Also feel free to contribute hints)
    Join the website → starlightps.org

🏗 In the future, I hope to work with others to build these exciting things:

  • An AI tool to predict the key insights/observations of problems
  • With enough data, summarize key insights/observations commonly used in certain types of contests (e.g. USACO Gold contests, codeforces problems with rating around 1900) to help people know the insights/observations required to successfully apply those algorithms to achieve their competitive programming goals 🏆 and give more structure 🧗.

💬 Join the community:

Join the Discord server: https://discord.gg/czgReQSpFz to share your input on how to improve this project/features to add!

🌐 Share this message:

Markdown format of this post, as well as a short text add, and an image promoting starlight are all available at https://tinyurl.com/starlightps-ads. All available under CC BY 4.0.

👐 Join the project (volunteer, open source)!

We are currently open source on GitHub: https://github.com/bkf2020. Licensed under AGPLv3.

Here is a Google Form to fill out with your qualifications if you are interested: https://forms.gle/txpWvcZwWxD1yVog6. I'm looking for machine learning engineers, web developers, web designers, and marketing/outreach.

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By butterflies, history, 20 months ago, In English

I'm confused on the editorial for 1666J - Job Lookup. View the editorial here

In the editorial for 1666J - Job Lookup, when transitioning from $$$a_{i,k - 1}$$$ and $$$a_{k + 1, j}$$$ to $$$a_{i,j},$$$ $$$c_{u, v}$$$ seems to be only added once (the number of messages going from $$$u$$$ to $$$v$$$, for all $$$u,v$$$ such that $$$i \le u \le k - 1$$$ and $$$k < v \le j$$$) even though the total cost should be $$$c_{u,v} \cdot d_{u,v}$$$. What is going on here?

Thank you for the help!

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By butterflies, history, 2 years ago, In English

EDIT: After talking to another person, I understand that if dp[k] gets updated by a certain cow, then that same cow CANNOT be used to update dp[k1]. So, this means we do not have to worry about updating dp[k1] if dp[k] gets updated.

Problem link: http://www.usaco.org/index.php?page=viewproblem2&cpid=839

Solution: http://www.usaco.org/current/data/sol_talent_gold_open18.html

In this problem, I am confused by this part in the solution

for (int j = 0; j < n; j++) {
    long long value = 1000*(long long)talent[j] - y*(long long)weights[j];
    int inc = weights[j];
    for (int k = w; k >= 0; k--) {
      int k1 = min(w, k + inc);
      if (dp[k] != -infinite) {
        if (dp[k1] < dp[k] + value) {
          dp[k1] = dp[k] + value;
        }
      }
    }
  }

The situation I’m having trouble on is if dp[k] gets updated by another cow, will dp[k1] also be updated?

First, if $$$k1 = W$$$ then we know that dp[W] will get updated for each cow.

Suppose the cow that updates dp[k] has weight $$$w$$$. Then, we know the value of dp[k - w] must be defined.

If dp[k - w] was defined BEFORE we visited the cow with weight $$$k1 - k$$$, then dp[k - w + k1 - k] = dp[k1 - w] gets updated.

Otherwise, dp[k - w] gets defined AFTER we visit the cow with weight $$$k1 - k$$$. We know dp[k1 - k] is defined, but what if dp[k1 - k] was used to compute dp[k - w]. How can we guarantee dp[k1 - w] is defined in this situation?

Thanks for the help!

Edit: bump

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By butterflies, history, 3 years ago, In English

Problem Link 737Div2 C

This is my solution. First, represent the $$$n$$$ numbers in binary. Each number has $$$k$$$ digits, where each digit can be $$$0$$$ or $$$1.$$$ Let $$$a_{i, j}$$$ represent the $$$j$$$th digit (from left to right) of $$$a_i$$$, where $$$a_i$$$ is represented in binary.

Now,

$$$a_1 \,\&\, a_2 \,\&\, a_3 \,\&\, \ldots \,\&\, a_n \ge a_1 \oplus a_2 \oplus a_3 \oplus \ldots \oplus a_n$$$

is true if for all $$$1 \le j \le k,$$$

$$$a_{1,j} \,\&\, a_{2,j} \,\&\, a_{3,j} \,\&\, \ldots \,\&\, a_{n,j} \ge a_{1,j} \oplus a_{2,j} \oplus a_{3,j} \oplus \ldots \oplus a_{n,j}.$$$

Let's consider the inequality for $$$j = 1,$$$ because others values of $$$j$$$ are similar.

$$$a_{1,1} \,\&\, a_{2,1} \,\&\, a_{3,1} \,\&\, \ldots \,\&\, a_{n,1} \ge a_{1,1} \oplus a_{2,1} \oplus a_{3,1} \oplus \ldots \oplus a_{n,1}.$$$

If more than one of $$$a_{i,1} = 0$$$ for $$$1 \le i \le n,$$$ then the left side of the above inequality is going to be zero. This requires the right side of the above inequality to be zero, so an even number of $$$a_{i,1}$$$ should be $$$1$$$.

Also, if all of $$$a_{i,1}=1,$$$ then that is another possible case. This only needs to be considered if $$$n$$$ is odd.

Now, using the above two paragraphs, there are

$$$\binom{n}{0} + \binom{n}{2} + \binom{n}{4} + \cdots + \binom{n}{n - n \mod 2} + n \mod 2 = \sum_{p = 0}^{\lfloor n/2 \rfloor} \binom{n}{2p} + n\mod 2$$$

ways to pick the $$$1$$$st digit for all $$$a_i.$$$

Using the Binomial Theorem on $$$(1+1)^n$$$ and $$$(1-1)^n,$$$ we can show that $$$\sum_{p=0}^{\lfloor n/2 \rfloor} \binom{n}{2p} = 2^{n - 1}.$$$

Thus, the number of ways to pick the $$$1$$$st digit for all $$$a_i$$$ is $$$2^{n - 1} + n\mod 2.$$$ Similarly, this is the number of ways to pick the $$$j$$$th digit for all $$$a_i.$$$

Since there are $$$k$$$ digits total in each of $$$a_i,$$$ the answer is $$$(2^{n - 1} + n \mod 2)^k.$$$

My code describes this approach, and I think it performs this approach correctly. Thus, I believe my approach to the problem is incorrect. Can anyone point out what is wrong?

I have also attached by code in case it is wrong.

Thanks for the help everyone!!

My code

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