Questions tagged [algorithm]

A puzzle related to algorithmics (a main concept in computer science).

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5
votes
1answer
1k views

How to programmatically solve math puzzle

I have this puzzle and I want to solve by code. I wrote simple code trying to brute force but it fail in one condition https://dotnetfiddle.net/cJyu3w Anyone know of a link or source how to solve ...
5
votes
2answers
107 views

Determine a polynomial with nonnegative integer coefficients with minimum queries

A friend of us makes up a polynomial with nonnegative integer coefficients. Our task is to find it out with a minimum number of queries. For each query we give him a nonnegative integer $L$ and he ...
8
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2answers
1k views

Stacking pancakes for your wife

You are cooking pancakes for your lovely wife. You want to sort the pancakes such that they increase in diameter as you move from the top to the bottom of the stack. The only operation you can perform ...
2
votes
3answers
244 views

Two of 18 coins are counterfeit

There are $n=18$ coins, and we know exactly $2$ of them are counterfeit. All counterfeit coins differ from normal coins in weight, but otherwise their weight is not known. They can be heavier or ...
1
vote
3answers
445 views

Move all the stones into a single cell of a 3x4 grid

A 3x4 grid contains a heavy stone in each cell. Walking from a cell to an adjacent cell (horizontally or vertically) without any stones requires 1 second. Moving one stone from a cell to an adjacent ...
14
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4answers
2k views

Emoji primes - what's the smallest positive integer this doesn't work for?

Driven by a silly conversation at work, here's the puzzle. Slack allows users to send emoji as a reaction to a message. Emoji are listed left to right in chronological order of reaction, and 'stacks' ...
3
votes
1answer
101 views

Reapply *some* stickers on scrambled cube

I have this weird cube which have some pieces printed on the plastic and some are detachable. The cube was scrambled not solved and it fell on the floor being cheap cube almost all detachable faces ...
2
votes
1answer
102 views

Looking for an old Rubiks cube algorithm

I learnt rubiks cube before the YouTube days from a blog. I do not find the algorithm anymore online but it is something like White cross White corners (except one) Second layer corners (except one) ...
5
votes
1answer
226 views

Brute-force solver for Gear Octahedron - flawed method?

I am working on a program to brute-force a LanLan Gear Octahedron I bought second-hand (and scrambled). I have no background in "cubing" and just fancied solving the problem. The structure comprises ...
11
votes
1answer
2k views

Worst way to solve Rubik's in one algorithm

If you apply the same algorithm over and over again the cube will be solved. I want to know what algorithm is the worst one (the one with the longest cycle) I have found RU (cycle of 60 times) I have ...
7
votes
1answer
264 views

Heavy-duty computing challenge — maximum-density word packing

Caution: This is a challenge for computers only. Humans are advised to stand well clear of the protective safety cage. There may be CPUs on fire before it's over. Introduction Nothing makes a ...
13
votes
12answers
2k views

2 Person Same Number Verification

Alice and Beth both receive a random integer from 1 through 10, inclusive. They only know the number that they are given. The two of them want to come up with an algorithm to check that their ...
5
votes
3answers
329 views

land of light bulbs

Leuks is the land of light bulbs, where the bulbs are leading a peaceful life, with no humans at all. Presently there are 100 residents . (Of course, they all are light bulbs!). Let $a_{1}, a_{2}, . ....
11
votes
2answers
2k views

Three knights searching for a princess in a castle

There is a castle with rooms arranged in a 4x4 square grid. The princess living in the castle sleeps in a different room each night, but always one adjacent to the one in which she slept on the ...
4
votes
1answer
329 views

Two knights searching for a princess in a castle

There is a castle with rooms arranged in a 3x3 square grid. The princess living in the castle sleeps in a different room each night, but always one adjacent to the one in which she slept on the ...
3
votes
1answer
68 views

Arranging people to be in a group with every other person at least once

There are 12 people. These people start in 4 groups - each with 3 people. They swap groups 4 times, so they are in a total of 5 groups. Is it possible for each person to be in a group with every other ...
0
votes
2answers
170 views

Hunting for treasure in 1-d grid [duplicate]

In a castle, there are N rooms in a line. Each room has a door to the two neighbouring rooms (or the one neighbouring room, for the rooms at either end). A treasure is hidden in one of the rooms. ...
8
votes
1answer
387 views

Cube Scrambling

Take a normal 3x3 rubiks cube (the Classic unmodded cube). I know the WCA method for scrambling is to pick a random (valid) cube state and calculate a sequence of moves to go from solved to that state,...
1
vote
2answers
271 views

Minimize sum of guesses to win lottery

Ten boxes are given with $a_1,a_2,a_3,a_4,a_5 ......a_{10}$ number of balls in them respectively .These boxes are randomly ordered but $a_1,a_2 .....a_{10}$ is told.We can arbitrary select a box and ...
2
votes
2answers
190 views

How to find number of times sequence element $1$ is approached and from where?

Consider a sequence $1,-1,-1,-1,-1,-1,...,-1$. Start at the first element and move down the sequence according to the following rules: 1) If you jump from a $-1$ to another $-1$, turn the latter into ...
7
votes
4answers
304 views

Savage Road Signs (Part 2)

Please read part 1 or this might be confusing Since part 1, you have replaced the stolen stickers and your daughter has forgiven you. The highway ended up being a full 700km long, so you are happy ...
2
votes
2answers
1k views

Finding numbers having exactly two distinct digits

We have $10^K$ road signs (numbered 0 through $10^K−1$). For each valid $i$, the sign with number $i$ has the integer $i$ written on one side and $10^K−i−1$ written on the other side. We need to ...
4
votes
1answer
2k views

Finding Round Integer

An integer is round if it is greater than $0$ and the sum of its digits in decimal representation is a multiple of $10$. Find an optimal procedure to compute the $N^\text{th}$ smallest round integer. ...
6
votes
1answer
242 views

$4\times4\times4$ Rubiks cube Top Layer Issue

The only way i am able to solve is to jumble the whole cube again. If you know the way to solve pls give images or algorithm.
6
votes
2answers
275 views

The CompuTaria Quest - A young Wizard's journey

Once Upon A Time In A Land FAR, FAR Away... Our adventure begins in the enchanted land called "CompuTaria". You are, "Binaryian" a 3rd year Wizard In Training. Today began like any other day - you ...
-4
votes
10answers
945 views

SafeCracker #3 - We've Been Blocked [closed]

Our Last Safe To Conquer Ok, team, this one might give us a little trouble. Nothing we can't handle though... let's go... This safe model is "The NevaCrak 9000" - the most secure safe there is. ...
5
votes
2answers
213 views

SafeCracker #2 - The Mission Continues

Thanks to an alert StackE user, we were able to get the first safe open. Mission Details This next safe is in a former employee's house. He is gone for now, so we have no time to spare. We weren't ...
3
votes
2answers
153 views

SafeCracker #1 - Look who's talking

The Plot You work for a tech company in Tampa, FL. Recently there was a break-in, and the company's trade secrets were stolen. Company PI have tracked the briefcase containing the secrets to the ...
2
votes
1answer
97 views

The NANNP Grid ( Not another Next Number Puzzle )

Simply figure out the last row...
33
votes
9answers
3k views

Wolves and sheep

All the sheep were living peacefully in the Land of Shewo. But suddenly they were struck by a danger. A few wolves dressed up as sheep entered the territory of Shewo and started killing the sheep one ...
17
votes
5answers
947 views

Blindfold Bingo

Congratulations, you have been selected from among the audience to compete in the fabulous Blindfold Bingo challenge! (cue annoying, yet catchy theme music.) Here you see our perfectly ordinary Bingo ...
5
votes
2answers
201 views

Find the result of this dual key cipher

I came up with a neat little cipher that I'm calling the dual key cipher. The basic premise is that there are two cipher keys that, when used together can decode the cipher text against a given ...
3
votes
2answers
154 views

The fantastic matrix

Here's another question that I have been asked in an interview lately. Let $M$ be an $n × n$ matrix whose values are $”+”$ and $”-”$. M is called fantastic if it is possible to make all it's values $”...
9
votes
1answer
259 views

Scoring Oracle: Bob easily wins, but how much?

Bob meets a magician with two bags and a chest on a bridge. The magician challenges him with the following enigma: Here is a bag A, holding 5080 pebbles. Here is another bag B. Most of the pebbles ...
4
votes
4answers
287 views

Weighing Counterfeit coins

There are $n=4$ coins and we know exactly $2$ of them are counterfeit. In $2$ weighings, how can we find which of the four coins are the counterfeit ones? Assumptions: the counterfeit coins look ...
8
votes
3answers
149 views

Creating a maze that is traversed by a pair of compasses

Normal mazes require you to move a point-like object from the entrance of the maze to the exit. I am wondering whether a different kind of maze would work as a puzzle: Imagine a maze printed on a ...
5
votes
3answers
267 views

Fill $N$ by $M$ grid with numbers in such a way that any given cells' neighbors are different

Create an $N$ by $M$ grid with numbers in such a way that satisfies following conditions: numbers should be integers that range from $1$ to $r$. for any cell $C$, all its adjacent neighbors (i.e. ...
5
votes
1answer
119 views

Shortest path for delivering packages [duplicate]

A version of the Travelling Salesman Problem, but with certain points. We are talking about a town where 8 canals run from the middle boathouse into the city. You can only travel one way on the green ...
9
votes
1answer
378 views

Puzzles like Sokoban?

I am looking for some puzzles like Sokoban or 15-puzzle but more difficult to solve and satisfy the following requirements: The number of possible moves at each step should be limited, let's say < ...
13
votes
4answers
368 views

20-Questions on a grid

Posted this on /r/puzzles too, none have given the right strategy as of now :) There is a square grid of width and height $m$. Three facts about the grid: Each cell has a value, and no two cells ...
7
votes
1answer
168 views

It's getting harder and harder for my friends to like me

What is the next number in this sequence? 2, 3, 6, 7, 9, 18, 25, 27, 54, 73, 97, 129, 171, 231, 313, 327, 649, 703, ... ? Hint 1 Hint 2 This is my first puzzle and I'm new to PSE, so feedback is ...
8
votes
4answers
446 views

Ten users, three lights but it's a chatroom

This is a variant of the classic problem of m prisoners n lights. (Example may be found here but note that the requirements are not exactly the same) The goal for you, however, is different. You want ...
2
votes
0answers
134 views

Ten users, ten deadly collars and three lights [duplicate]

One day, 10 puzzling.SE users, including you, find yourselves in a horrible prison. Each of you has a deadly collar, presently lethal. It is safe to take off only when all of the 10 collars have been ...
6
votes
1answer
183 views

A couples therapy mixer situation

During couples-group-therapy, where two therapist and multiple couples consisting of two people each are present and we all sit on chairs forming a circle in the middle of the room. We often discuss ...
3
votes
1answer
95 views

How can these people cross the bridge? [duplicate]

There are 4 people that must cross an old dilapidated bridge at night, All four walk at different speeds: There is a young teenager that can cross the bridge in 1 minute. There is teenager's older ...
24
votes
7answers
6k views

Hacking an electronic keypad

You are a spy trying to break into an enemy facility. The back door is protected by an electronic keypad lock. You know that this particular lock is opened by a four digit code. Any stream of button ...
1
vote
1answer
269 views

Scheduling Meetings

I came across this problem in real life and thought it could be made into an interesting puzzle. I will enjoy seeing how my eventual solution could be improved! Here's the situation. There ...
1
vote
3answers
1k views

Is my 5x5 cube on an “illegal” position?

I've never met this postion before, and i'm starting to think it's an "illegal" one because i lend it to a friend before and he said he had to glue some fallen stickers. Am i missing an alorithm or do ...
1
vote
0answers
236 views

Finding all possible solutions of a japanese sums puzzle

I'm trying to think of an algorithm that gives out all possible solutions to a japanese sums puzzle. It's not an a college assignment or anything, I'm giving puzzles to my cousin for fun, but want to ...
0
votes
1answer
362 views

Is there a name for this Rubik's cube algorithm?

$RUR'U RU2R'$ I use this algorithm to: permute UL and UF edges (messing up corners) orient LL from a fish (possibly using its mirror) orient pairs of LL corners by combining above algorithm with its ...