Questions tagged [algorithm]
A puzzle related to algorithms (a main concept in computer science). Puzzles may ask for an algorithm as an answer or require the analysis of a given algorithm.
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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 ...
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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' ...
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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.
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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The NANNP Grid ( Not another Next Number Puzzle )
Simply figure out the last row...
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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 ...
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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 ...
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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 ...
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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 $”...
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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 ...
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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 ...
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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 ...
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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. ...
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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[...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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Is there an algorithm for the Rubik's 360?
Is there an algorithm to help me solve the Rubik's 360?
Usually I just do it at random, but I rarely succeed.
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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 ...
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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 ...
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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 ...
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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:
...
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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 ...
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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
...
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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 *|*...
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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 ...
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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.
...