We use cookies to ensure you have the best browsing experience on our website. Please read our cookie policy for more information about how we use cookies.
There is are a couple of very convenient features of calendars that many solutions here apear unaware of. Here's my solution.
"""PythonProjectEuler+Problem#19:CountingSundaysbySevenconcept:Every400years,thecalendarcyclerepeats.Therefore,byfindingallsunday-the-firsts(STFs)inanyrangeof400years,onecandeducethenumberofSTFsinanyotherrange.Forconvenience,wecancalculatetherange2000-1-1to2399-12-31sinceitwillallowustofindanyyear'splaceinthecyclebysimplytakingtheyearmod400.Herafter"relative year"referstotheyearmod400forstartingyearsandstartyearmod400+(endyear-startyear)forendingyears.Thedayoftheweekforanygivengregoriancalanderdatecanbecalculatedusingasimpleformula(seetheweekday(y,m,d)functionbelow).SinceweonlycareaboutSTFs,weonlyneedtocheckthefirstofthemonthofeachmonth.Theresultsarestoredin"lookup"asabooleanlist,whereeachvaluerepresentsamonthfromrelativeyear0(e.g.2000or11804211600)throughrelativeyear399(e.g.2799or2810399).TrueindicatesthefirstofthemonthwasaSunday.Sincetheenddateisnevermorethan1000years,12monthsand31daysfromthestartyear,wecanrepeatthisrangeby4forconvenience.Thus,therelativestartandenddatesalwaysfallwithintherangeofthelookuplist.Theconveniencefunctionym(y,m)takesarelativeyearandmonthandreturnstheassociatedindexinthelookuplist.Finally,givenastartandenddate,wesimplyfindtherelativeyearsforthosedates,andsumthevaluesofthelookuplistbetweenthedates(inclusive)."""frommathimportfloordefweekday(y,m,d):"""y:yearm:month(1=March-12=Februaryoffollowingyear)d:dayreturn:dayofweek(0=Sunday-6=Saturday)reference:https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html#:~:text=Here%20is%20a%20standard%20method,the%20day%20of%20the%20month.byAlexLopez-Ortiz"""## adjest the month number, shifting Jan and Feb back one yearm-=2ifm<1:m+=12y-=1## Split the year into the c=Century and y=two digit yearc,y=divmod(y,100)return(d+floor(2.6*(m)-.2)-2*c+y+y//4 +c//4) % 7defym(y,m):"""y:yearm:monthreturn:indexoftheyear,monthinthelookuplist"""return12*y+(m-1)defspan_count(y0,m0,y1,m1):"""y0:startyearm0:startmonthy1:endyeary2:endmonthreturn:totalSTFsinthegivenrange"""## find the distance from y0 to y1y1-=y0## find the relative starting yeary0%=400## find the relative ending yeary1+=y0## sum the values between the two dates (inclusive)returnsum(lookup[ym(y0,m0):ym(y1,m1)+1])## defining the lookupgloballookuplookup=[]foryinrange(400):forminrange(1,13):lookup.append(weekday(y,m,1)==0)## repeat the lookup so that relative start/end years always fall within## the range of the lookup listlookup=lookup*4## parse inputsforiinrange(int(input())):y0,m0,d0=[int(n)fornininput().split(' ')]y1,m1,d1=[int(n)fornininput().split(' ')]## if the start date is after the first of the month, we can just start on## the first of the following monthifd0>1:m0+=1ifm0==13:m0=1y0+=1## find the resultprint(span_count(y0,m0,y1,m1))
Cookie support is required to access HackerRank
Seems like cookies are disabled on this browser, please enable them to open this website
An unexpected error occurred. Please try reloading the page. If problem persists, please contact support@hackerrank.com
Project Euler #19: Counting Sundays
You are viewing a single comment's thread. Return to all comments →
There is are a couple of very convenient features of calendars that many solutions here apear unaware of. Here's my solution.