Questions tagged [algorithm]

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

Filter by
Sorted by
Tagged with
9
votes
2answers
1k 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 ...
3
votes
1answer
288 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
59 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
158 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. ...
2
votes
2answers
172 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 ...
6
votes
2answers
240 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 ...
7
votes
1answer
310 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
251 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 ...
7
votes
1answer
348 views

Avoiding Incest and Intergenerational Mating

On the planet of Caturn, God created $m$ male cats and $f$ female cats, each with zero stripes. At any time, two cats of opposite genders can mate, giving birth to a cat with a gender of the parents' ...
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. ...
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 ...
83
votes
7answers
18k views

Why does this solution guarantee that the prince knocks on the right door to find the princess?

I found this puzzle online: On the top floor of a castle lives a princess. The floor has 17 bedrooms arranged in a row. Each bedroom has doors connecting to the adjoining bedrooms as well as to the ...
7
votes
4answers
289 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 ...
30
votes
8answers
2k 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 ...
6
votes
1answer
227 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.
5
votes
2answers
201 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 ...
-4
votes
10answers
924 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. ...
3
votes
2answers
141 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
90 views

The NANNP Grid ( Not another Next Number Puzzle )

Simply figure out the last row...
17
votes
5answers
723 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 ...
27
votes
7answers
2k views

23 Clones and Two Lightbulbs

Rise and shine, Mister Bond. James awoke to find himself yet again imprisoned by an evil genius. At least, that's what he presumed. He was alone in a room with a strange device: it consisted of a ...
5
votes
2answers
183 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
147 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
255 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
271 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 ...
7
votes
3answers
116 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
250 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. ...
4
votes
1answer
510 views

Generalisation of Nim

I'm asking for a general formula/algorithm that can be used in such a game. There are $n$ piles, with varying number of pebbles. The number of pebbles in each pile is given by an array from $pile[...
5
votes
1answer
114 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
273 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 < ...
10
votes
2answers
1k views

Let's deal with “Names in Boxes” Safely

I met a puzzle, which is basically well known 100 Prisoners' Names in Boxes , but... it has an algorithm, which gives prisoners 100% chance to survive! This is achieved by a small change in the ...
13
votes
4answers
352 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 ...
12
votes
1answer
799 views

What is the optimal first move in Mastermind?

For a given number of positions/holes and a given number of colors, which initial guess eliminates the most possibilities for the solution at a minimum? For 4 positions, it's AABB. What is it for 5, ...
7
votes
1answer
164 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
425 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
121 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
180 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 ...
11
votes
3answers
36k views

What is the Official notation on rubik's revenge(4x4)?

When solving a 4x4 cube you have specific notation to inner and outer lines, like R = Clockwise outer right and r = Clockwise ...
11
votes
3answers
1k views

The Generous Taco stand

There are a group of people standing in line for a taco stand. This taco stand is special in that it's slogan is "The older you are, the more you get!". To make sure though that there isn't any funny ...
3
votes
1answer
90 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 ...
23
votes
7answers
5k 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
1answer
1k views

Algorithm for solving the permutation puzzle Tricky Animals

I have developed a game called Tricky Animals where the goal is to reorder the animals in the right order with three permutations: $A = (1,2), X = (2,3,..,n-1), B = (n-1, n)$. The game can be played ...
1
vote
1answer
214 views

When will inverting an algorithm allow it to function the same as the original?

Let's say I have this zperm algorithm: R' U' R U' R U R U' R' U R U R2 U' R' U2 Now, let's suppose I invert it. U2 R U R2 U' R' U' R U R' U' R' U R' U R Assuming the cube is in a state of its pll ...
1
vote
3answers
745 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
217 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
304 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 ...
3
votes
2answers
230 views

Figure out when a data usage cycle restarts

Your cell phone carrier sends you a text message when you have reached your data limit (which you know) for the month, after which you are charged for extra data usage. Question 1: You want to ...
-4
votes
2answers
636 views

Sub-30second solving the $3\times3\times3$ Rubik's cube

I just wanna learn cubing under 30 secs. Please help me:( As i've already learned the Beginner's method. Is there any easiest way to learn the CFOP method as i am unable to understand this method. I ...
0
votes
2answers
2k views

Measuring volumes with oil drums of 8 and 5 litre [duplicate]

You have two drums of capacity 8 litre and 5 litre and a resource of oil, can you use these two drums to give 1 litre, 2 litre, 3 litre, 4 litre, and 6 litres and 7 litres to any customer? If yes, ...