I stumbled across an interesting probability problem about half an hour ago. https://en.wikipedia.org/wiki/100_prisoners_problem
Essentially, there are 100 boxes, drawers, etc, each with a unique number between 1-100 inside of them. There are also 100 prisoners. Each prisoner has 50 chances to find the box with their number. If even one does not, they all fail. The chances would be abysmally low if they all randomly picked 50 boxes, but there's a better strategy.
Each prisoner first opens the box labeled with their own number.
If this box contains their number, they are done and were successful.
Otherwise, the box contains the number of another prisoner, and they next open the drawer labeled with this number.
The prisoner repeats steps 2 and 3 until they find their own number, or fail because the number is not found in the first fifty opened drawers.
This should increase their chances to above 30 percent with the way everything can fall into a loop
I glanced through this and decided it was interesting enough to quickly code out in python, but I'm getting a really interesting (and probably wrong) result. Could someone take a look at the code?
import random
def begin(p=False): #print
prisoners = [i for i in range(100)]
boxes = prisoners.copy()
random.shuffle(boxes) #we now have a list of shuffled boxes. index represents box num
if p: #prints
for i,num in enumerate(boxes): #i=index, num=content of box. Just to print it out
print(i,num)
def run(p=True): #print
results ={"Success":False, "NumSucceed":0, "NumFail":0 }
for prisoner in prisoners: #Try every prisoner
fail = True #check if they fail
choice = boxes[prisoner] #initialize choice as box with prisoner num
for i in range(49): #49 becaues first choice counts as well
if choice==prisoner:
fail = False
break
choice = boxes[choice]
if fail:
results["NumFail"] +=1
else:
results["NumSucceed"]+=1
if results["NumSucceed"]==100:
results["Success"] = True
if p: #just if I choose not to print results
print(results)
return results
for i in range(100):
begin()
run()
How many ever times I run it I always get a failing result where 17 prisoners succeeded and the rest failed (I randomize the rotation of the boxes each time too). Does anyone know why? I hope I didn't just make some stupid error somewhere and waste your time lol, if you do look through this I'd appreciate it
Couple of notes first.
Make sure you keep locality/scope in mind with variables. You have a begin() function thats used to declare your variables for the entire script, but they aren't declared globally so when the other method runs, it won't be able to find the variables to declare in begin()
not sure how you got it to run as is tbh
so let's scrap the method and just initialize our prisoners and boxes
import random
prisoners = [i for i in range(100)]
boxes = [i for i in range(100)]
now you can put the shuffle in your run method, since only boxes need to be randomized and conceptually, randomizing boxes would be the first thing done each time the prisoner dilemma happens.
def run(p=True): #print
random.shuffle(boxes)
results ={"Success":False, "NumSucceed":0, "NumFail":0 }
# ...
I ran a couple times and got 20-40 out of 100 total runs where all prisoners found their tag
nice little riddle there.
I tried to execute your code, but ran into an NameError exception due to a name space problem. Basically both prisoners and boxes within your code are only defined while begin() is running.
I've used your solution and modified it a bit:
import random
from operator import countOf
PRISONERS = 100
class PrisonerProblemSolver:
def __init__(self) -> None:
# Generate prisoners and boxes
self.prisoners = list(range(PRISONERS))
self.boxes = self.prisoners.copy()
random.shuffle(self.boxes)
# collector for results
self.results = {"Success": False, "NumSucceed": 0, "NumFail": 0}
def solve(self):
for prisoner in self.prisoners:
fail = True
choice = self.boxes[prisoner] # tries own box first
for _ in range(49): # remaining attempts
if choice == prisoner:
fail = False # will not die
break
choice = self.boxes[choice] # follows and hopes
if fail:
self.results["NumFail"] += 1
else:
self.results["NumSucceed"] += 1
return self.results["NumSucceed"] == PRISONERS
if __name__ == '__main__':
solver = PrisonerProblemSolver()
results = []
# Let's look at 100 prisons
for _ in range(100):
solver = PrisonerProblemSolver()
results.append(solver.solve())
# how successful were they in dying?
print(countOf(results, True))
Hope this helps.
Best regards
Related
I have a problem regarding a competition question I'm attempting to do. Here is the question (its a bit long)
""""
Welcome aboard, Captain! Today you are in charge of the first ever doughnut-shaped spaceship, The
Circular. There are N cabins arranged in a circle on the spaceship. They are numbered from 1 to N in
a clockwise direction around the ship. The ith and the (i + 1)th cabins are connected. So too are cabin
1 and cabin N.
Currently the ith cabin has Ai crewmates, however the spaceship cannot depart unless there are exactly
Bi crewmates in this cabin.
To achieve this, you have the power to pay crewmates to change cabins. You can pay a crewmate $1 to
move to an adjacent cabin. A crewmate can be asked to move multiple times, provided that you pay
them $1 each time.
What is the fewest dollars you must pay before you can depart? It is always be possible to depart.
""""
https://orac2.info/problem/aio22spaceship/ (the link to the intereactive Qs)
I searched the web and i found no solutions to the Q. My code seems to be infinite looping i guess but im not sure as i cant see what cases the sit uses to determine if my code is right.
Heres my code
#!/usr/bin/env python
import sys
sys.setrecursionlimit(1000000000)
#
# Solution Template for Spaceship Shuffle
#
# Australian Informatics Olympiad 2022
#
# This file is provided to assist with reading and writing of the input
# files for the problem. You may modify this file however you wish, or
# you may choose not to use this file at all.
#
# N is the number of cabins.
N = None
# A contains the initial number of crewmates in each cabin. Note that here the
# cabins are numbered starting from 0.
A = []
# B contains the desired number of crewmates in each cabin. Note that here the
# cabins are numbered starting from 0.
B = []
answer = 0
# Open the input and output files.
input_file = open("spacein.txt", "r")
output_file = open("spaceout.txt", "w")
# Read the value of N.
N = int(input_file.readline().strip())
# Read the values of A and B.
input_line = input_file.readline().strip()
A = list(map(int, input_line.split()))
input_line = input_file.readline().strip()
B = list(map(int, input_line.split()))
AM = A
#AM is my modifying set
# TODO: This is where you should compute your solution. Store the fewest
# dollars you must pay before you can depart into the variable
while AM != B:
#Check if the set is correct
#notfound is a testing variable to see if my code was looping due to input error
notfound = True
for i in range(N):
#Check which places needs people to be moved
while AM[i]>B[i]:
notfound = False
#RV and LV check the "neediness" for each half's people requirements. I check how many people
#are needed on one side compared to the other and subtract the "overflow of people"
RV = 0
LV = 0
for j in range(int(N/2-0.5)):
#The range thing makes sure that if N is odd, im splitting the middle but if N is even, i leave out the end pod
RV += B[(i+j+1)%N]-AM[(i+j+1)%N]
LV += B[(i-j-1)%N]-AM[(i-j-1)%N]
answer +=1
if RV>LV:
AM[i]+=-1
AM[(i+1)%N]+=1
else:
AM[i]+=-1
AM[(i-1)%N]+=1
print(AM,B)
if notfound:
break
print(answer)
# Write the answer to the output file.
output_file.write("%d\n" % (answer))
# Finally, close the input/output files.
input_file.close()
output_file.close()
please help i really neeed to know the answer, driving me mad ngl
Welp, there aren't any resources online and I've tried everything. I think the problem might be that because of my solving method, passengers may be flicked between two pods indefinitely. Not sure since i could make a case that demoed this.
also my post probably is messy since this is my first time posting
I'm running a python script that will display messages on a board. One of the subroutines that I've created is supposed to grab a random line from a small text file, and display that line. It mostly works, except after looping a few times, it gets stuck on the same number, and just displays the same thing over and over.
I am running this in Python 2.7, on a Raspberry Pi in Raspbian. I am using this github as the base for the project, and added lines of my own to it:
https://github.com/CalebKussmaul/Stranger-Things-Integrated
This is part of a halloween display that will be Stranger Things-themed, so the preloaded messages have a reference to the show. I noticed this issue the other day, and have been pouring over the internet to try and figure out what the problem could be. I've tried doing different methods of selecting a randomized number, including some in some similar (but different) threads on this site. All of them produce exactly the same issue.
Below is the subroutine I created:
def preloaded_messages():
print "Preloaded Messages thread is loaded."
global displaying
while True:
if not displaying:
with open('preloaded_messages.txt') as f:
lines = len(f.readlines())
rgn = random.randint(1,lines)
msg = linecache.getline('preloaded_messages.txt', rgn)
print "rng: ", rgn
print "total lines: ", lines
print "line: ", msg
print "displaying from preloaded_messages.txt: ", msg
display(msg)
time.sleep(10)
And here's my preloaded_messages.txt file:
help me
im trapped in the upside down
leggo my eggo
friends dont lie
run /!
hopper is alive
rip barb
demogorgon is coming /!
mouthbreather
When I run it, my output is like this:
rng: 6
total lines: 9
line: hopper is alive
rng: 2
total lines: 9
line: im trapped in the upside down
rng: 9
total lines: 9
line: mouthbreather
...
rng: 9
total lines: 9
line: mouthbreather
the first few times are always random (and the number of times it successfully randomizes varies), but when it gets on 9, it just stays there for as long as I let it run. I am at a loss as to why it works the first few times, but not once it gets to 9.
EDIT: Interestingly, as I've been writing this, I also tried adding a blank line at the end, and while it looked like it'd be stuck again, as it did that one three times in a row, then it finally moved to others. I'm not sure how that changes things. And ideally, I'd rather not have the blank line in there, as it eats up time displaying nothing. So it'd be nice to fix the issue. Anyone have any ideas?
It is reseeding the random generator. See line 49 of stranger.py in the https://github.com/CalebKussmaul/Stranger-Things-Integrated: random.seed(i).
The color_of function should be written as:
def color_of(i):
"""
This function generates a color based on the index of an LED. This will always return the same color for a given
index. This allows the lights to function more like normal christmas lights where the color of one bulb wont change.
:param i: index of LED to get color of
:return: a pseudorandom color based on the index of the light
"""
_random = random.Random(i)
rgb = colorsys.hsv_to_rgb(_random.random(), 1, 1)
return int(rgb[0] * 255), int(rgb[1] * 255), int(rgb[2] * 255)
To create its own Random instance with the given seed rather than reseeding the Random instance that is a singleton in the random module.
This appears to work for me. Note that I'm seeding the RNG.
import time
import random
from datetime import datetime
def preloaded_messages():
print("Preloaded Messages thread is loaded.")
displaying = False
while True:
if not displaying:
with open('preloaded_messages.txt') as f:
random.seed(datetime.utcnow())
text = f.read().splitlines()
msg = random.choice(text)
print("line: ", msg)
# print("displaying from preloaded_messages.txt: ", msg)
time.sleep(10)
if __name__ == "__main__":
preloaded_messages()
I am trying to use a while loop to create object to populate a list of a user defined type until a certain condition is met. I want to assign a value to each object based on the number of iterations the loop has completed. For example:
class WalkingPeeps:
def___init___(self):
self.location = 0
def leftAt(self,time):
self.tleft = time
def changePos(self):
self.location += random.choice([1, -1])
objectList =[]
location_reached = False
time = 0
while not location_reached
objectList.append(WalkingPeeps())
for x in objectList:
x.tleft = time
if x.location == 20:
location_reached = True
time+=1
print("Person left at: ",x.tleft)
print("Person arrived at: ", time)
However, when it runs, it just set the time the object was created to one less than when the person reached 20. Any pointers? Hints? Thanks in advance.
In python, loops do not define their own scope. When you write
for x in objectList: ...
There variable x is created. At each step in the loop, the variable is updated. When the loop ends, the variable is not destroyed. Therefore, when you print x.tleft, you're printing the time on the last x, which by definition is 20, since you break the loop only when x.tleft == 20.
Furthermore, since you loop over every single element at each phase and update its time, you're setting each elements time to the most reccent time. Therefore, all elements have time == 20, when you terminate. What you mean, I believe, is to only update the last element
What I think you want to print, to check that your loop is working is,
for obj in objectList:
print( obj.tleft )
You would then see the expected behaviour
You also have many errors, including some syntax errors and some that make the code enter an infinite loop. This is the version I worked with, in good faith (try and make sure that the the only bugs in your code are the one's you're asking about!)
class WalkingPeeps: pass # None of the methods were relevant
objectList =[]
location_reached = False
time =0
while not location_reached:
objectList.append(WalkingPeeps())
x = objectList[-1]
x.tleft = time
# you need to check tleft, not location; location is never set
if x.tleft == 20:
location_reached = True
time+=1
print("Person left at: ",x.tleft)
print("Person arrived at: ", time)
for person in objectList: print(person.tleft)
A far more readable and concise version of this code would be:
class WalkingPerson:
def __init__(self,time=0):
self.time=time
objectList = [WalkingPerson(t) for t in range(20)]
As a beginner programmer, I don't know how to conceptually think about brute-forcing. My mind can't really fathom how to write code that will try every possibility. My answer is recursion, but as you will see below, I have failed.
If you need the full source
I have a problem that I want to solve. Here is a code snippet (there are other functions, but no reason to include them here, they just do background work):
def initiate(seen):
step_segment = []
STATS = [250,0,0,0,13,0]
if len(seen) >= 256: # when to escape the recursion
return seen
while (len(step_segment)) < 128:
step_segment, STATS = take_step(step_segment, STATS)
if STATS[5] == "B": # if there is a battle
if STATS[0] in seen: # if battle has been done before
status = seen.index(STATS[0]) # get battle status:
status += 1 # which is next to step_id (= G or B)
if seen[status] == "B": # for seen battles, try Glitch ("G")
step_segment = do_glitch(step_segment, STATS)
else:
step_segment, STATS = do_fight(step_segment, STATS) # fight
seen = seen + [STATS[0],STATS[5]]
time = get_frames(step_segment)
print "\nTime:", time
print seen
return initiate(seen)
The goal: I want to produce a list of every possible decision through a segment, along with how long it takes.
Description:
I will take a step (There's only one direction: forward). Every time I take a step, my stats are updated. This takes a step and updates the stats: step_segment, STATS = take_step(step_segment, STATS)
A list of steps taken, along with the stats, are kept in
step_segment. This is so I can 'undo' an arbitrary amount of
steps, if I want. To undo a step call the function:
step_segment, STATS = undo_step(step_segment, STATS)
I can see how long my current route has taken by doing: time = frames(step_segment).
At some point, I will get into a Battle. I get into a battle when
STATS[5] == "B"
When there is a battle I have to make a decision, I simply have two choices: i. Fight the
battle (B), or, ii. Run away glitch (G).
If I want to Fight, I do: step_segment = do_fight(step_segment, STATS). This also records that I chose to fight, along with the stats, in step_segment. (So I can undo it, if i want).
If I want to Run Away Glitch, I do: step_segment = do_glitch(step_segment,STATS).
I want to see every possible combination of Glitch & Fight (the only two choices, when I reach a battle).
At the moment, my code is very bad and does not try all of the possibilities. I don't really know how to code for all possibilities.
So, that's why I'm here. How can I implement a way of trying all possibilities when facing a decision?
I understand the problem has exponential amount of possibilities, but thankfully the maximum number is pretty small (<1024).
I have read about tree traversal, but I have no idea how my problem can be put into that format. Eg, I don't know what a 'node' would be in my problem. I actually don't know what anything would be... That's why I'm asking.
I have written a small coin flipping program for Home work Python, it will choose one of two values; Heads or Tails at random and print them, the loop iterates 10 times then stops. As I understand it the only way to count the number of repetitions of some words is to place the words in an array or a split variable string and then run a pre-written cnt. Click Here to see that discussion.
I need to know how you get Python to take the random value it produced and then save it into an array according to the number of iterations of the for loop(in this case x number of iterations).
Here is the variable name and the two options:
coin = ["Heads", "Tails"]
Here is the code for the coin flipper core:
#Flipping core :)
def flipit(random, flip, time, comment, repeat):
time.sleep(1)
print("It begins...")
print("\n")
for x in range(0, 10):
print("Flip number", x + 1)
print(random.choice(comment))
time.sleep(1)
print(random.choice(coin),"\n")
time.sleep(2)
print("\n")
from collections import Counter
counting = []
cnt = Counter(counting)
cnt
print("Type startup(time) to begin flipping coins again")
If you do feel like refining the code please do if you have the time, but all I need is a method that I can put into the overall program that will make it run properly.
Please don't worry about the random comment, that was for a bit of fun.
I have pasted the whole program on PasteBin, Click Here for that.
Thank you for reading this and my gratitude to those who respond or even fix it.
Edit:
Just for reference I am a bit of a newbie to Python, I know some things but not even half of what the people who answer this will know.
Solution:
I have managed to make Python "read" the random value using a per-iteration if statement in my for loop, using if statements I have added 1 to the respective variable according to the random.choice.
Here is the flip core code:
def flipit(random, time, comment, headcount, tailcount, side):
time.sleep(1)
print("It begins...")
print("\n")
for x in range(0, 10):
print("Flip number", x + 1)
side = random.choice(coin) # get the random choice
print(random.choice(comment))
time.sleep(1)
print(side) # print it
if side == "Heads":
headcount += 1
else:
tailcount += 1
time.sleep(2)
print("\n")
print("You got", headcount, "heads and", tailcount, "tails!")
print("Type start() to begin flipping coins again")
resetheadtail()
resetheadtail() is the new function I have added to reset the variables at the end of the program running.
For the full code click Here!
Thanks all who helped, and those who persevered with my newbieness :)
#comment necessary for edit, please ignore
I think what you want to do is:
flip = random.choice(coin) # get the random choice
print(flip) # print it
counting.append(flip) # add it to the list to keep track
Note that you will need to move counting = [] to before your for loop.