Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [algorithm]

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

5
votes
3answers
156 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
99 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
191 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
337 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
151 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
396 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
114 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
170 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
84 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 ...
22
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
266 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
522 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
197 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
225 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
228 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 ...
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 ...
0
votes
2answers
1k 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, ...
-5
votes
2answers
513 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 ...
18
votes
4answers
2k views

Consecutive Towers of Hanoi

Consider the following variant of the Towers of Hanoi puzzle. There are six pegs. One of the pegs has a stack of $n$ differently sized disks, sorted by size so the smallest disk is at the top. All ...
2
votes
1answer
128 views

How many moves are at least needed to change the order of cubes to a arbitrary order? [closed]

We have several cubes that are ordered as in the picture below: What is the smallest number of moves with which we are able to reach every possible order? Only the order of the cubes in the ...
2
votes
1answer
212 views

Doubts about algorithm

Hello I came across a really good algorithm perfect for a minigame I'm making. When I was trying to implement the algorithm I stumbled with some doubts and I can't the algorithm right. I'm talking ...
1
vote
1answer
190 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 ...
4
votes
1answer
2k views

Is it possible to scramble a Rubik's cube so that each face has no more than 2 squares of the same color?

So the complete conditions for this scrambled cube can be described alternatively as the following: Each face has less than 3 squares of the same color, which leads to 1a. Each face has 5 or 6 ...
1
vote
1answer
435 views

The swap puzzle

The swap puzzle Place small coins heads up on the squares marked H and tails up on the squares marked T. Swap the positions of the Heads for the Tails in as few moves as possible. There are two ways ...
6
votes
2answers
942 views

Is there a simple algorithm for solving Kami 2 puzzles?

I'm finding my life has been consumed by Kami 2, partly because I seem to have achieved some "insight" and am able to solve the puzzles reliably, almost always on the first try. The rules are simple: ...
2
votes
1answer
382 views

Algorithm to Solve Puzzle - Advice Needed

Given the following letters arranged in a circular pattern. A B E C D Each letter can merge with any of its opposite letters to form an adjacent ...
12
votes
1answer
585 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, ...
2
votes
1answer
304 views

sort n balls by knowing the lightest in one query

Suppose there are $n$ balls with different weights and let $b$ be an integer between $2$ and $n$. There is a machine which, given a set $S\subset\{1,2,3,\dots,n\}$ of size at most $b$, can tell you ...
0
votes
5answers
472 views

Pipe and socket problem

Given a set of n pipes of different sizes and n sockets of different sizes. There is a one to ­one mapping between pipes and sockets, meaning that a pipe can fit into only one socket. Match pipes and ...
1
vote
1answer
751 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
2answers
269 views

Find other swords down the waterfall

This is another old pattern I generated with a 1D cellular automaton: To me it looks like a sword hidden in a waterfall. The neighborhood of a cell looks like this: What is the rule behind this ...
15
votes
5answers
4k views

Can you recreate this fractal I randomly made?

This fractal looks relatively simple, but how would you generate it? On a smaller scale: I made it using a 1D cellular automaton with a four cell neighborhood: ...
-4
votes
3answers
315 views

Bartenders' beer-table error-correction code

At a pub, a friend spotted our table number being 412; there were nowhere near 400 tables. We mused if it could include a checksum so the bartender could tell if customers gave an invalid number. I ...
4
votes
3answers
511 views

What numbers fill the blanks in 3*3 grid? [closed]

I have a puzzle that I did not know how it could be solved Which numbers should be filled on the blank spaces ? I only figure out that 4 + 20 = 24 and 1 + 20 = 21 then 8 + 20 = 28 I am not sure ...
19
votes
1answer
1k views

Mystery operation

In a future not so far way, Earth archaeologists find on a far away planet a fragment from a long lost civilization. This fragment involves an unknown operation *|*...
10
votes
3answers
3k views

How do I memorize parity algorithms for higher-order Rubik's cubes?

I know how to solve a Rubik $4\times4\times4$ or $5\times5\times5$ or bigger, but I have problem with a specific algorithm: the parity error. What's the shortest parity algorithm for $n\times n\times ...
5
votes
3answers
359 views

Place 16 queens in a $16\times 16$ board peacefully, also in subboards!

What is the smallest number, $n$ in which $n$ queens can live in a $n\times n$ board peacefully? Of course not more than 8. ☺ (read about the eight queen puzzle) But this was not the question. ...
1
vote
2answers
331 views

Calculating column number based on Excel alpha column reference [closed]

Here's a super fun brain teaser!!! Can you give me a mathematical equation to calculate the column number of a Microsoft Excel column, given the alphabetic column reference? Let X, Y, & Z ...
1
vote
1answer
4k views

Check sudoku solvability

With a blank grid, I put and number (1-9) any cell, the Sudoku has n solutions. I continue filling any blank cells with numbers that satisfy the constraints, so the Sudoku still has many solutions, ...
3
votes
3answers
1k views

Sorting 4 numbers using “maximum” & “minimum” between 2 numbers

I'm having some trouble solving this thing. You're given an unlimited number of "black boxes" which will return the maximum or the minimum between 2 inputs. The goal is to compare/sort 4 numbers ...
10
votes
2answers
1k views

3x3x3 Rubik's Cube Illegal State

After I learned how to solve a 3x3 Rubik's Cube and a 4x4 Rubik's Revenge, I began challenging myself to solve the cubes to different states rather than the normal solid sides. For instance, I'd solve ...
-4
votes
2answers
95 views

Last number in barcode [closed]

Find solution, how work algoritem for last, control number in 8 places barcode. Here is some results: Here we got last number 8 Here we got last number 7: Here we got last number 5 What is last ...
10
votes
1answer
491 views

Half-reverse operation on binary strings

Is there an algorithm that you can apply twice to an input string of $0$s and $1$s in order to reverse it? In other words, is there a function $f : \mathrm B \to \mathrm B$ on the set of binary ...
1
vote
0answers
103 views

Rubik's Cube Master Algorithm [duplicate]

I've been thinking about this question for a while, but I have no idea how to approach it. I don't know what the answer is. The question: What is the shortest finite set of moves that, when repeated,...
6
votes
1answer
255 views

Placing markers in grid and minimize similarity of rows

Imagine a game on a grid of $m$ rows and $n$ columns. Player One will place a fixed number $r$ of markers in each row. Player Two will select the two rows which maximize the number of columns having ...
3
votes
1answer
351 views

How do I solve this F2L case quickly?

I have been unable to find a solution for this f2l case. It takes about 3 seconds to do, and I do it really slowly. Basically, the f2l case is solved, but the edge is inverted. The way I do it right ...
20
votes
2answers
1k views

Desegregate the Knights

You are given a 3 by 3 chessboard with a knight on each corner, where the knights in the top row are black and in the bottom row are white. On each turn, you may move a knight of either color (the ...
29
votes
5answers
3k views

Switch The Knights

On a small $ 4 \times 3$ chessboard, the top row is filled with black knights and the bottom row with white knights. On each move, you may move one knight (as it moves in chess) to an unoccupied ...
11
votes
4answers
281 views

Rank the Fencers

There are five fencers. Each has a particular skill level, all of which are different. When two fencers duel, the one with the higher skill level always wins. How many duels do the fencers need to ...
25
votes
6answers
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 ...